Estimating the Economic Value of Soundscapes in Nature-Based Tourism Destinations: A Separation Attempt of a Pairwise Comparison Method

: Recent soundscape research is notable owing to the increasing demand for “multisensory” tourism experiences. However, the traditional economic value assessment of tourism destinations mostly takes each type of landscape as a whole for measurement, and it has been challenging to separate the soundscape from the whole landscape. Therefore, research on the economic value of soundscapes is still lacking. This study chose the characteristic soundscape of the Qiantang River tide as the research object, and tried to apply the pairwise comparison method to calculate the separation coefficient of the soundscape from the overall landscape. The results showed that the separation coefficient of the soundscape was 0.138 and the economic value of the Qiantang River tide soundscape was between CNY 315.145 million (USD 48.7 million) and CNY 333.841 million CNY (USD 51.6 million). Finally, we discuss the effectiveness of the separation methods, the differences in willingness to pay between the interviewees, and the sustainable use of the natural soundscape resources in tourism destinations.


Introduction
All Member States of the United Nations adopted the 2030 Agenda for Sustainable Development and the Sustainable Development Goals (SDGs) in 2015 [1]. Tourism plays an increasingly important role in the specific objectives of sustainable economic growth and the sustainable use of resources [2,3]. China has always attached great importance to sustainable tourism, and was early to build a national system of protected areas that included nature reserves, forest parks, and scenic spots [4]. The continuous development of tourism has driven economic growth in various regions, and China's annual tourism revenue reached CNY 6.63 trillion in 2019, with an annual increase of 11.1% [5]. To date, some studies have explored the impact of tourism on local economic, social, and environmental development from the perspective of space and landscape perceptions [6].
Mainstream geography and tourism studies in space and landscape have been dominated by visual traditions [7,8], over multisensory perception dimensions such as touch, taste, and hearing [9,10]. As the second important sense after vision [11], hearing plays an important role in information acquisition, spatial perception, and the formation of environmental cognition [12,13]. The esthetic quality of soundscape is the key to tourists' satisfaction [14]. At the same time, natural sound as a resource is in urgent need of clear management and protection [15]. The study of soundscape has gradually attracted the attention of scholars. The term soundscape refers to the auditory property of a landscape, that is, the sum of the sounds received by human ears in a specific environment [16,17].
The study of soundscape has been gradually extended to the fields of ecology [18,19], urban and rural planning [20,21], geography [22,23], and tourist experiences [24,25]. Under the background that "multisensory" tourism experiences receive more attention, soundscapes play an increasingly important role in scenic planning and sustainable development [26]; therefore, the proportions of the soundscapes in overall economic value of scenic spot resources need further study, and a separation method has not been well established [27].
As one of the necessary conditions for developing tourism in all regions, the reasonable assessment of the economic value of tourism resources has always been an important issue in the conservation and sustainable development of natural resources [28]. The method of evaluating the economic value of resources originates from the theory of "costbenefit analysis" proposed by William Petty [29]. With the continuous improvement and maturity of the research on the concepts of consumer surplus and opportunity cost in welfare economics, scholars have calculated the non-use value of public products based on natural resources, and the structure of tourism resource value has become increasingly clear. Then, it derives the travel cost method (TCM) to measure consumers' explicit preference, and the method represented by the contingent valuation method (CVM) to measure consumers' declarative preference. Thus, explicit preference and declarative preference to measure the use and non-use values of resources allow to finally obtain the overall economic value of resources [30]. TCM and CVM, as the two most widely used evaluation methods in academic circles [31], have been used to measure forest resources [32,33], natural reserves [34][35][36], cultural heritage [37][38][39], coastal recreational areas [40,41], and other resource values. These methods have played an important role in the conservation of natural resources and the perception of cultural resource values. They have laid the foundation for soundscape value assessment work and have also confirmed the importance of this work.
Based on a review of the existing research results, we found that soundscapes have gradually become an important resource for the sustainable development of tourism attractions. A proper assessment of resources can better promote their conservation and use, but the traditional assessment of the economic value often considers the landscape as a whole. In the General Plan for the Reform of Ecological Civilization system, it is clear that natural resource ownership should be separated from the right to use [42]. Soundscapes are a characteristic resource; therefore, it makes sense to reasonably assess the economic value of soundscapes to guide the practice of the marketization of natural resource use rights. As a traditional characteristic natural soundscape, Qiantang River tide is majestic, and the sound of the tide is earth-shaking, while Yanguan Tide Resort Park is one of the best places to watch the first-line tide. Therefore, based on the existing research theories, this study took Yanguan Tide Resort Park as a case and accomplished the following work: (1) Comparing and constructing soundscape separation coefficients based on the perspective of "multisensory" experiences through a pairwise comparison method and tourists' direct scoring; (2) assessing the economic value of the Qiantang River tide soundscape; and (3) discussing the rationality of the soundscape value assessment approach and its role in the planning and development of scenic spots. This study aimed to clarify the monetization estimation of natural soundscape resources, innovate the property rights system of natural resources, and give full play to the advantages of natural soundscape resources in the sustainable development of tourism destinations.

Soundscape and Natural Soundscape
The term "soundscape" was originally proposed by Schafer [43]. In his concept, the definition of "soundscape" has the characteristics of broad sense, musical dominance, and environmental orientation [16]. With the deepening of the research, the definition of "acoustic environment perceived, experienced, and understood by individuals or society" given by the International Standardization Organization (ISO) explains soundscapes from three different scales: human, sound, and environment [44]. Different from the physical characteristics of "acoustic environment," the concept of "soundscape" emphasizes the "user experience and perception" of the local acoustic environment [14,45]. As an important dimension of the beauty in tourism destinations, soundscapes meet the differentiated needs of tourists in terms of esthetic experiences [46]. Natural soundscapes are a part of soundscapes, referring specifically to the synthesis of sounds from nature [47]. Because they are typically perceived to be pleasant and relaxing, natural soundscapes are usually regarded as one of the core attractions of tourism destinations [48].
In the United Nations Educational, Scientific and Cultural Organization (UNESCO) Convention on Intangible Cultural Heritage, scholars consider the deep-seated interdependence between the natural heritage represented by natural soundscapes and the intangible cultural heritage [49]. Indeed, soundscapes are playing an increasingly important role in the conservation of natural and cultural heritage [50]. Tourists have different preferences for natural soundscapes, and a correct understanding of the acoustic value of scenic spots can help to promote local green tourism development [51].
Tourism geographers have researched soundscapes from the space and landscape perspectives, mainly focusing on noise pollution, tranquility, tourism experience, and music tourism, concluding that noise pollution harms tourism destinations [52]. By calculating the contingent valuation method, the price of reducing noise pollution in national parks that tourists are willing to pay to enter can be obtained [53]. In terms of the value of the tranquility of scenic spots to tourists, scholars mainly focus on the relationship between tranquility and tourist motivation [54] or tourism satisfaction [55]. Scholars are also concerned about the relationship between soundscape and tourism experiences. Tourists' experiences of the acoustic environment are based on their perception of the physical properties of the acoustic environment [56], while a positive combination of the acoustic environment and the traditional visual experience plays an important role in improving tourists' experiences [53]. In terms of music tourism, as a special form of sound, the music itself is the core attraction of tourism destinations, such as music festivals, which play a significant role in shaping the brand image of the destination by enhancing tourism experiences and promoting economic and social development [57]. Scholars have further discussed tourists' corresponding behavior driving mechanism based on soundscape cognition [47]. However, there are relatively few studies on valuable natural soundscapes in tourism destinations. In addition, there is a lack of reasonable methods to evaluate the economic and recreational value of natural soundscapes. Therefore, current research urgently needs to supplement the existing comprehensive evaluation model of soundscape resources, which is mainly based on subjective experience evaluation.

Economic Value Assessment Methods
TCM and CVM are currently the most mainstream methods for assessing the economic value of resources and landscapes [31]. As a display preference method based on field survey data, TCM derives many analysis models according to the types of destinations and travel cost measurement methods, such as the zonal travel cost model (ZTCM) [58], the individual travel cost model (ITCM) [59], the gravitational travel cost model (GTCM) [60], the hedonic travel cost model (HTCM) [61], the random utility model (RUM) [62], and travel cost interval analysis (TCIA) [63]. These methods are widely used in the value assessment of natural and cultural heritage [39]. For a more intuitive and comprehensive presentation of the consumer's willingness to pay, the use of CVM for the calculation of non-use values has gradually increased. CVM constructs a reasonable hypothetical market through questionnaire design and uses mature guidance and evaluation techniques to obtain the interviewees' maximum willingness to pay for recreational resources [64].
With the deepening of research, to address problems such as the statistical data validity and variable multicollinearity of TCM methods [65,66], and the deviation caused by different guidance evaluation techniques in CVM methods [64], scholars have also carried out corresponding corrections and improvements to ensure the rationality and accuracy of the assessment. All of these methodological improvements provide a good reference for work on the economic value assessment of soundscapes.

Research Design
The core problem to be solved in measuring the economic value of soundscapes is how to separate the economic value of soundscapes from the overall landscape value. Thus, this study is divided into two parts: The determination of the separation coefficient of soundscapes and the calculation of the total economic value of scenic spots. The economic value of a soundscape can be obtained by multiplying the separation coefficient of said soundscape by the total economic value of a scenic spot (see Figure 1). In terms of the soundscape separation coefficient, the Qiantang River tide landscape needs to be separated from the overall landscape. Then, the soundscape needs to be separated from the multidimensional senses. Finally, the separation coefficient of the Qiantang River tide soundscape can be obtained by multiplying the two factors. Currently, there are few related research results, and most studies focus on the differences between soundscapes and visual landscapes in tourism experiences [27]. Therefore, this study improved the analytic hierarchy process (AHP) [67], collected score data of the first three impressive landscapes and senses listed by the subjects, compiled the mathematical calculation program by using database technology, calculated the proportions of the Qiantang River tide and soundscape, and finally obtained a reasonable soundscape separation coefficient. At the same time, to verify the effectiveness of the separation coefficient obtained by the pairwise comparison method, this study set up direct scoring of the items by tourists in the questionnaire, which refers to the existing literature on the separation mode of glacier resources in whole scenic spots [68]. Then, through a comparison of the results obtained by the two different methods, the optimal method to determine the separation coefficient is discussed. In measuring the overall economic value of scenic spots, the existing research theories and methods are more mature. Based on the research mentioned above, this study comprehensively applied TCM and CVM to measure the total economic value of scenic spots.
The questionnaire design was divided into the following three parts. The first part collected the basic demographic information, such as the age and sex of the subjects. The second part was mainly related to the separation coefficient of the soundscape. The questionnaire adopted the pairwise comparison method to separate the overall landscape of the scenic spot. First, it listed 17 types of landscapes marked by the official tourist map of the scenic area, such as Yanguan's first-line tide, Zhanao Tower, tide-watching sculpture, and the Tide-Watching Poem Pavilion. Then, it set up multiple choice topics for tourists for choosing which landscapes they see in the scenic area. Afterward, the tourists chose the three most impressive landscapes and compared their importance. To solve the problem of soundscape separation from multidimensional senses, the design idea of the questionnaire was the same as that mentioned above, allowing tourists to choose the three most-used senses in terms of sight, hearing, touch, smell, taste, and other senses when enjoying the Qiantang River tide and to make an important comparison between the two choices. Finally, to verify the validity of the separation coefficient obtained by the pairwise comparison method, the questionnaire was designed to allow tourists' direct rating and filling in of the blanks; e.g., "If there were no Qiantang River 'first-line tide' landscape in the scenic spot, how likely would you be to visit the scenic spot?" and "If the total value is 100%, what is the proportion of vision, hearing, and other multi-senses?" The third part mainly dealt with the calculation of the overall value of the scenic spot. It collected the necessary information about the total cost of tourists' departure place, transportation, food, accommodation, and tour time required by the travel expense method. Meanwhile, for the CVM, the questionnaire used the payment card method to collect the maximum willingness to pay of the respondents' existing value, the selection value, and the heritage value in the scenic spot. The specific questionnaire is shown in Appendix A.

Pairwise Comparison Method
In calculating the soundscape separation coefficient, this study adopted the pairwise comparison method based on AHP and used the data of the three most impressive landscapes and the most frequently used sensory scores collected in the questionnaire, as well as the paired importance comparison data (extremely unimportant, unimportant, equivalent, more important, and extremely important). It then compiled a calculation program, from which the proportion of tidal landscape and hearing of Qiantang River was obtained [69]. The specific methods are as follows: First, to ensure that the subsequent calculation was more accurate, the paired comparative evaluation values 12 , 13 , and 23 of landscape (sensory) 1 and landscape (sensory) 2, landscape (sensory) 1 and landscape (sensory) 3, and landscape (sensory) 2 and landscape (sensory) 3 were transformed into proportional sequences in the questionnaire. To avoid the contradictory situation of paired comparison values caused by the environment and the quality of the interviewees, this study used a series of judgment sentences to screen the validity of the data. After screening the validity of the data, we used the root method to calculate the weights 1 , 2 , and 3 of landscape (sense) 1, landscape (sense) 2, and landscape (sense) 3.
Finally, because this study took the interviewees as a whole, the answers of all of the individuals of the interviewed groups partly reflect the tourists' preferences for landscapes and sensory uses. Therefore, although each interviewee only proposed his or her preferred three landscapes and senses, many interviewees proposed different combinations of answers so that the total number of preferred landscapes and sensory uses of the interviewees was not less than three. The landscape and sensory use weights of the interviewed groups were calculated as shown in Equations (7)-(9): where is the sum of the evaluation weights of landscape (sense) j of all respondents; is the evaluation weight of interviewee i for landscape (sense) j; is the total evaluation weight of all interviewees for all landscapes (senses), so is the pairwise comparison weight of landscape (sense) j. To sum up, the separation coefficient of the Qiantang River tide soundscape can be obtained by multiplying the Qiantang River tide landscape weight by the hearing weight ( × ℎ ).

TCIA and CVM
In terms of specific TCM model selection, the zonal travel cost model was used to divide the interviewees' tourist sources into several regions, taking the estimated travel cost of each tourist source area as the independent variable and the visit rate of each source area as the dependent variable to estimate the tourism demand function. However, the proportion of tourists outside the province in the Yanguan Tide Resort Park in 2018 was only 46%. The actual situation of the tourist source in this case was contrary to the analysis idea of the zoning travel cost model, so it was not suitable to use this method. At the same time, 69% of the respondents came to the scenic spot for the first time, and the rate of revisiting tourists in the scenic spot was low. If the individual travel cost model is used, the demand function cannot be estimated due to the lack of variable dispersion. Therefore, based on the actual research situation of this case, we introduced the travel cost interval analysis model, which directly uses the total travel cost as the standard of segmentation of the tourist market. This avoided any defect in which the travel costs of tourists from the same source region are regarded as consistent in the zonal travel cost model.
Travel cost interval analysis assigns N number of respondents in different intervals according to total travel cost (TC), namely, [TC0, TC1], [TC1, TC2], …, [TCi, TCi+1], …, [ TCn, +∞], a total of n + 1 consumption intervals, and the number of respondents in each interval is . Therefore, based on this assumption, when the travel cost is , the tourists in this area and those who are willing to pay higher fees are the interviewees who are willing to travel in this case. At this time, the tourism demand under the travel cost level is = ∑ ＝ , and the willingness travel rate ( ) of each interval is / . As a result, the interviewees' travel willingness curve = ( ) can be obtained by curve regression fitting of the travel expenses and willingness travel rate in each section. Based on the travel willingness curve, the consumer surplus of each interviewee ( ) in the i-th segment can be obtained as follows: . Then it can be known that the total consumer surplus is CS = ∑ × =0 . Finally, the formula for calculating the total recreation value (RV) of a scenic spot is , , and represent the consumer surplus value of the sample, the travel expense of the sample, the number of samples, and the total number of tourists in the year.
Given the accuracy of guidance assessment technology, scholars have made many reasonable improvements to CVM and, accordingly, guidance assessment technology [70,71]. Considering that domestic interviewees are generally unfamiliar with the CVM survey method, and it is difficult to understand the questionnaire, such as multi-boundary dichotomous choice in a short time [72], this study chose the payment card guide mode, which is easy to understand and appropriately increases the bid value of the payment card according to the pre-survey results, to reasonably control the deviation that may be caused by the setting of the bidding starting point.

Study Area
The Qiantang River, located in Zhejiang Province, flows eastward into the East China Sea. The tide at its estuary is well-known globally (Figure 2). With the change in geographical location, Yanguan in Haining has become the best resort for watching the tide since the Ming Dynasty. Yanguan Tide Resort Park has always been said to be a place for "hearing the sound before seeing the tide." The specific location of the scenic spot is shown in Figure 3. Currently, relying on its unique natural wonders and perfect infrastructure, the scenic spot attracts many tourists every year (3.5 million in 2019). There is no research to calculate the economic value of Yanguan Tide Resort Park or to evaluate the economic value of the Qiantang River soundscape; hence, this study attempted to evaluate the economic value of the Qiantang River tide soundscape.  Different from some traditional soundscape studies, which focus on noise control to ensure that tourists can obtain natural tranquility [54], the soundscape of the Qiantang River tide is louder in terms of its physical properties, and tourists can hear the shocking tidal sound before the tide comes. Schafer, founder of soundscape theory, believes that soundscape consists of different prospect sounds, background sounds and signal sounds [16]. The prospect sound is the most characteristic sound in a certain region. For the soundscape of the Qiantang River tide, the natural sound of the tide rolling and lapping at the dam is the prospect sound. Background sound refers to all kinds of sound elements except prospect sound in tourism environment. For natural tourism destinations, the human soundscape created by human activities is the background sound. The signal sound is the sound that attracts people's attention, except for emergencies, the scenic spots generally control the signal sound. The physical properties of the soundscape can be described mainly in terms of loudness, pitch and timbre [73]. This paper collected the sound of the Qiantang River tide in July 2019, and used the Python toolkit Librosa to draw a spectrogram of the sound. The frequency, decibel, and other indicators of the sound at different times of the specific tide passage are shown in Figure 4, where decibel and frequency can represent the loudness and pitch of the sound respectively. The time period from 42 s to 48 s in the figure belongs to the interval when the tide reaches the observation point. Tourists have different preferences for the sound environment under different engagement modes [9], they appreciate the Qiantang River tide soundscape more for the excitement and new experiences [15], and close experiences of the soundscape can provide tourists a more shocking and awe-inspiring experience. This also reasonably explains tourists' strong willingness to pay. The data of this study were mainly based on the first-hand data of the field investigation of Yanguan Tide Resort Park in Haining. The first field investigation was conducted in May 2019. The research team took an initial overview of the development in the study area and adjusted the payment card bid value data based on the pre-survey results. The research team then conducted a sample survey in Yanguan Tide Resort Park from 20 July to 28 July 2019. A total of 400 questionnaires were distributed and 374 were recovered, of which 364 were valid, resulting in an effective recovery rate of 91%.

Calculation of the Soundscape Separation Coefficient
Based on the research ideas, this article first used the pairwise comparison method to calculate the proportion of the Qiantang River tide landscape. After excluding invalid interviewee data, the study calculated the weights of three landscape dimensions in the interviewees' questionnaire and established a database of interviewees' selections, as well as the ratio of the 17 scenic spots listed in the questionnaire. Equations (1)-(6) were used to calculate the respective weights 1 , 2 , and 3 of landscapes 1, 2, and 3. Finally, the perceptual weights of the interviewees to all types of landscapes in the scenic area could then be measured through Equations (7)-(9). The specific results are shown in Table  1. From the results, we can see that the first-line tide landscape of the Qiantang River occupies the main position in the weight of the comparison value of the interviewees among the 17 listed landscapes, reaching 48.733%. Among the listed landscapes, the weight of scenic spots and iconic landscapes were also relatively high, such as Jinyong Academy, Haishen Temple, and Zhan'ao Pagoda. The landscapes built in the later period were not given more attention; these included the Ancient City Planning Exhibition Hall and infrastructure. Thus, tourists seemingly prefer the authentic local landscape for sightseeing. In the second step, we calculated the proportion of hearing in multiple senses as 28.395% (Table 2). It was not difficult to find that the proportion of vision and hearing in the senses used by the interviewees reached nearly 90%, which is consistent with the conclusion that vision and hearing are the two most important senses in traditional studies. In this study, tourists paid increasing attention to the multisensory tourism experience represented by hearing in tourism, and so vision only accounted for nearly 60% of the multisensory pairwise comparison value results, which is much lower than that of previous studies [11]. Conversely, the proportion of senses such as hearing and smell significantly improved, which fully reflects the differences in tourists' experiences and preferences of natural sound features represented by the Qiantang tide. This also highlights the important role of soundscapes in the process of tourist experience and scenic spot development. Finally, by calculating the pairwise comparison values of the Qiantang River tide landscape and hearing senses, respectively, the separation coefficient of the soundscape was determined to be approximately = × ℎ = 0.487 × 0.284 = 0.138. Because the pairwise comparison method is different to the traditional expert matrix comparison method, the consistency test of the analytic hierarchy process cannot be used for to test the data validity. Therefore, based on the abovementioned research ideas, this study set up direct scoring items for tourists. Through the weighted average calculation, the direct score weight of the tourists could be obtained, and the validity of the results obtained by the pairwise comparison method could be tested by comparing the results of the two different separation methods. It is subjective and random for tourists to directly judge the proportions of the Qiantang River tide landscape in the scenic spot. It was difficult for the interviewees to understand the literal meaning of the questionnaire. Therefore, when asking specific questions, this study adopted the reverse method. The questionnaire asked about the possibility that tourists would still visit without the Qiantang River tide landscape, so as to reverse the importance of the Qiantang River tide landscape in the scenic spot as a whole. The specific calculation results are shown in Table 3. The probability of interviewees visiting was 36.808%; thus, it can be inferred that the weight of the Qiantang River tide landscape was 63.192%. The proportion of hearing senses was 28.954%. By comparing the weight results of the two separation methods (Table 4), we found that the two separation methods had high similarity in the proportion of hearing, and the validity of the pairwise comparison method could be effectively confirmed. However, at the same time, we found that compared to the calculation results of the proportions of the Qiantang River tide, the results of the tourists' direct scores were higher than those of the pairwise comparison method. The main reason is that, contrary to multisensory separation, the interviewees were more familiar with the use of senses and the number of senses was relatively lower, while this questionnaire provided tourists more landscape options, and tourists had a greater degree of choice. The tourist direct scoring method directly asked the interviewees the proportions of the Qiantang River tide landscape in the landscape of the scenic spot, and it was difficult for some interviewees to understand all of the landscape types involved in the scenic spot; thus, it was difficult to take into account the comprehensiveness and to form a correct judgment. Finally, the Qiantang River tide landscape accounted for a relatively high proportion in the tourist direct scoring method. This study found that the separation coefficient of the Qiantang River tide soundscape in Yanguan Tide Resort Park was approximately 0.138.

Economic Value Calculation of the Scenic Spot Based on TCIA
Based on the TCIA research method, it was necessary to investigate the interviewees' total travel expenses. The tourists were divided into two major markets: Group tourists and individual tourists. Different questionnaire items were designed for the two types of tourists, and the specific calculation formulas were as follows: In Equation (10), represents individual tourists' total travel costs, including round-trip transportation expenses, accommodation expenses, meals, and other expenses. In Equation (11), represents group tourists' total expenses, including the expenses paid to travel agencies and other separate expenses. To solve the problem that most of the interviewees are multi-destination tourists, scholars have made many attempts, such as the cost-sharing method [74] and scenic spot combination methods [75]. Based on previous studies, this study used the cost-sharing method to adjust the total travel expenses by taking the proportion of the number of stay days in the scenic spot to their total travel time as the sharing coefficient, in order to calculate the travel expenses of a single destination. Then, based on the basic research design of TCIA, this study conducted partition processing according to the travel cost data of the interviewed samples, and calculated the number of interviewed samples , the tourism demand , and the willingness demand rate of each interval. The specific results are shown in Table 5. According to the zoning data of the travel costs in Table 5, a scatterplot of the willingness demand rate and the interval travel cost could be obtained. The willingness demand rate curve is nonlinear, as seen from the scatterplot. The higher the interval travel cost, the lower the interviewees' willingness to travel demand rate, which is consistent with reality. This study selected four models, namely, linear, logarithmic, quadratic, and exponential, and took the willingness demand rate as the dependent variable and the interval travel cost as the independent variable to fit the curve. A summary and the parameter estimation results of the four models are shown in Table 6. By comparing the parameter estimates of the four models, the value explained by index model with the highest R (0.964) and the F value (797.579) could be selected as the interviewees' demand curve of travel intention for Yanguan Tide Resort Park; that is, = 0.719 × −0.002 ; furthermore, the logarithmic conversion result was ln = −0.330 − 0.002 . It is known that under the assumption that only travel costs affect interviewees' travel intention demand rate, for every 1 CNY increase in travel costs, the logarithm value of the travel intention demand rate decreases by 0.002 percentage points. Then, the consumer surplus of the interviewees in each section could be calculated from the tourism willingness demand curve and Equations (12) and (13) (Table 7).

Economic Value Calculation of the Scenic Spot Based on CVM
In this study, 16 bid values were set for the interviewees to choose by using payment card guidance. First, 310 respondents were willing to pay a certain fee for the sustainable existence of the scenic spot, accounting for 85.165% of the respondents; 275 respondents were willing to pay a certain fee for themselves or others to still have the opportunity to appreciate the scenic spot, accounting for 75.549%. Finally, 305 respondents were willing to pay a certain fee for leaving the scenic spot resources as a legacy for future generations, accounting for 83.791%. The interviewees generally had a strong willingness to pay for the non-use value of scenic resources, but there were obvious differences in the willingness to pay for different non-use values. In the same context, the respondents were more willing to pay for the existence value and heritage value of the scenic spot, while the willingness to pay for the choice value was relatively low.
After analyzing the interviewees' socioeconomic characteristics and their willingness to pay, the results of the single factor analysis of variance (Table 8) show that gender and education had an obvious influence on the interviewees' willingness to pay. In contrast, age, occupation, and monthly income had little influence. Taking the willingness to pay for heritage value as an example, 75.316% of the 158 male respondents versus 90.291% of the 206 female respondents were willing to pay. In terms of education level, with the continuous improvement of the respondents' education level, their willingness to pay for heritage value increased continuously. The willingness to pay increased from 50.000% of primary school and below, 76.744% of junior high school, 81.250% of senior high school/technical secondary school, and 85.047% of junior college or undergraduate education to 94.595% of graduate students and above. This shows that with the continuous improvement of the national education level, the non-use value of natural resources will be increasingly recognized. Under the social background of the continuous improvement of national quality education, the non-use value of natural resources represented by soundscape resources will also receive more attention. Through a statistical survey of the respondents' maximum willingness to pay, we found that the respondents are willing to pay from CNY 1 to CNY 900. The specific willingness to pay and the number of statistics are shown in Table 9. As a result, the tourists' per capita willingness value to protect the natural resources of Yanguan Tide Resort Park was determined to be CNY 137.168. Combined with the data of the 3.5 million tourists in the scenic spot, the overall non-use value of Yanguan Tide Resort Park was CNY 480.088 million. The existence value, choice value, and heritage value accounted for 29.652%, 29.879%, and 40.469%, respectively. Thus, the tourists represented by the respondents had higher recognition of the heritage value of the scenic spot, and they had a stronger willingness to pay for the motivation to leave the natural wonder of Qiantang River tide landscape for future generations.

Economic Value Calculation of the Qiantang River Tide Soundscape
Based on the above calculation results, this study multiplied the separation coefficient of the tide soundscape with the calculation results of the overall economic value of the scenic spot. Finally, the economic value of the Qiantang River tide soundscape could be calculated. The overall economic value of the scenic spot measured by TCIA was CNY 2.413 billion. At the same time, the separation coefficient of the Qiantang River tide soundscape obtained by the pairwise comparison method was approximately 0.138, which shows that the economic value of the Qiantang River tide soundscape was CNY 333.841 million. The total non-use value of the scenic spot measured by CVM was CNY 480.095 million. By combining it with the soundscape separation coefficient, the non-use value of the Qiantang River tide soundscape was calculated as CNY 66.434 million.
Through the analysis of the TCIA, we can see that the market value of the Qiantang River tide soundscape represented by the interviewees' total explicit travel cost was CNY 248.711 million, created directly by the soundscape for tourists to use. The consumer surplus value of the Qiantang River tide soundscape, represented by the consumer surplus in various consumption areas, was CNY 85.130 million. This belongs to the non-use value category, in which the Qiantang River tide soundscape of the scenic area indirectly participates in the socioeconomic ecosystem, both of which constitute the economic value of the Qiantang River tide soundscape. The non-use value of the soundscape measured by CVM was CNY 66.434 million. By comparing the consumer surplus results of TCIA, we found that that the result was slightly larger than that of CVM. The ratio of the two evaluation results was approximately 1.281, and so the error was relatively small, which effectively proves the rationality of the selection and calculation results of the two methods. Therefore, if TCIA is used alone, the economic value of the Qiantang River tide soundscape in a scenic spot would be CNY 333.841 million. On the premise that the existence value, choice value, and heritage value can fully summarize the non-use value of scenic resources, the Qiantang River tide soundscape's economic value can be obtained as CNY 315.145 million by combining TCIA with CVM. Therefore, it can be further inferred that the Qiantang River tide soundscape's economic value is in the range of CNY 315.145 million (USD 48.7 million) to CNY 333.841 million (USD 51.6 million).

Discussion
In recent years, although research on the "multisensory" tourism experiences of tourists represented by the sense of hearing has received increasing attention from scholars, there is still a lack of in-depth research on soundscapes. At the same time, because of the complexity of the separation method, the economic value of traditional tourism destinations is generally measured as a whole, making it difficult to implement a thematic study on the economic value of soundscapes. Therefore, this study selected the characteristic natural soundscape of the Qiantang River tide as the research object, applied the pairwise comparison method to the calculation of the separation coefficient of the economic value of the soundscape, and integrated the travel cost method and the conditional value method to assess the economic value of the Qiantang River tide soundscape in the scenic area. The ultimate research purpose was to provide targeted guidance for the sustainable development of soundscape-featuring tourism destinations.

Theoretical and Methodological Implications
First, in the context of gradual attention to soundscapes, the problems of reasonably assessing the economic value of soundscapes and how to separate the value of soundscapes from the overall landscape value of the scenic area have not been effectively solved [27]. The first innovation of this study was to try to apply the pairwise comparison method to the separation of a soundscape from the whole landscape, and to improve the test method of the validity of the separation coefficient when the data consistency test index is difficult to apply. This paper calculated the separation coefficient of the Qiantang River tide in the overall landscape and the auditory separation coefficient of the tourists' multidimensional senses, respectively, and finally obtained the overall separation coefficient of the Qiantang River tide as 0.138. This method can be used to assess the economic value of soundscapes and can be used as a reference for future research on landscape separation. At the same time, the authors cross-checked the reasonableness of the separation coefficient results by setting up a direct rating option for tourists in the questionnaire, which provided new ideas for data reasonableness testing work.
Second, the phenomenon of "visual tyranny" is prevalent in traditional tourism research, where researchers generally focus on the visual aspects of tourism destinations and ignore the prevalent value of soundscapes [47]. Another innovation of this study was defining the economic value composition of natural soundscape and scientifically calculating the proportion of hearing in multisensory tourism experiences from the perspective of tourists' perceptions. Visual and auditory senses were still the two most important senses for visitors to enjoy the scenery, with a combined proportion of over 90%. We found that the proportion of auditory senses was approximately 28.395%, which significantly increased compared to the proportion of traditional research results [11]. The main reasons for this are twofold: On the one hand, the tide is a natural soundscape and has been described as "waves like thunder" since ancient times, making the sound of the tide more distinctive than other traditional scenic spots and more likely to leave a deep impression on visitors; on the other hand, the proportion of senses represented by smell and touch in this study increased compared to the results of traditional studies, which reveals that modern travelers are gradually emphasizing the "multisensory" tourism experience. Researchers need to conduct more in-depth research on "multisensory" experiences to accommodate the different types of tourists' needs, and ultimately to effectively enhance the nonuse value of soundscape resources.
Finally, in the traditional economic value assessment of scenic spots, although two mainstream methods-namely, TCM and CVM-have been developed, measurement errors have been a difficult topic for scholars to avoid, especially in terms of nonuse values [64]. In this study, the value assessment model was innovated by combining the two methods. At the same time, the measurement model was reasonably selected to improve the accuracy of the assessed values in view of the low proportion of out-of-province tourists and the low revisit rate of the case study group. As this study focused on the special object of soundscapes and the Qiantang River tide, no research was conducted to systematically measure the economic value of Yanguan Tide Resort Park. Unlike previous studies on economic value assessment, the calculation results can be compared with the existing research results to analyze the reasonableness of the calculation results [76]. This paper compared the results of both TCIA and CVM in the relatively large error area of measuring the non-use value of landscapes, with a ratio of 1.281-a relatively small error. The relatively small non-use value of the soundscape obtained by CVM compared to the results obtained by TCIA is mainly due to the influence of errors in aspects such as hypothetical conditions and information asymmetry in the respondents' willingness to pay bootstrapping process [77,78]. However, compared to TCM, which calculates consumer surplus based on the travel willingness demand curve, CVM provides a more comprehensive and intuitive picture of respondents' actual willingness to pay [79], while the three non-use values (existence value, choice value, and heritage value) of soundscapes can be classified in more detail and have stronger practical implications.

Managerial Implications
In ancient times, people were more concerned with the "sound of the waves" of the Qiantang River tide, while nowadays, the description of the Qiantang River tide is more inclined to "spectacular" and the value of the soundscape of the Qiantang River tide is not fully appreciated. As soundscapes can have a more direct and rapid impact on tourists than visual landscapes [16], this study highlighted the importance of soundscapes in the development and management of scenic areas through a reasonable monetary assessment of their value, responding to tourists' demand for a "multisensory" tourism experience. In the planning and management of scenic areas, tourism development is resource-driven [80], the management of scenic areas should clarify the importance of soundscapes and focus on preserving and promoting the Qiantang River tide's unique soundscape in the planning and management process, trying to use more auditory elements to attract tourists. At the same time, considering the continuous commercial development of the scenic area, the natural soundscape is affected by the noise of tourists and other factors. The management should control the number of tourists promptly. Reasonable diversion should be monitored in real time for decibels, frequencies, and other element frequencies to maximize the protection of the sound environment of the natural soundscape to give tourists a more intense and intuitive experience of the natural soundscape and to promote sustainable development of scenic areas.
The study area, Yanguan, not only has very characteristic natural soundscape resources, but also has a lot of "tide-watching" historical and cultural heritage derived from the tidal soundscape. In the research results, we found that the historical and cultural relics represented by Zhanao Tower and Haishen Temple were also core attractions of the scenic spot. Therefore, according to the spirit of the UNESCO Convention for the Safeguarding of Intangible Cultural Heritage [49], the same attention should be paid to the natural sound landscape resources and the cultural heritage of "tide-watching" in the daily management of the scenic spot. The scenic spot can take measures such as setting up a natural soundscape museum to record the size of the daily tide from the perspective of sound. The ultimate goal is to achieve the interdependence and sustainable development of natural soundscapes and intangible cultural heritage.
In the survey on the nonuse value of scenic areas based on the conditional value approach, more than 80% of the respondents were willing to pay a certain amount for the conservation of the area's existence and heritage value, and the willingness to pay gradually increased with increasing education levels. In the context of an increasingly educated society, managers need to encourage visitors to experience the charm of natural soundscapes, while combining humanistic soundscapes such as traditional folk music and music festivals to continuously raise the importance people attach to the value of soundscapes. This will promote the transfer of natural resource use rights in scenic areas and the market-oriented operation of natural resource management, as well as accelerate further practical exploration and institutional reform of ecological civilization.

Limitations and Future Research
This study has some limitations. First, because tourists can only choose the three most important options for a two-by-two comparison, the options they chose do not necessarily summarize all of their preferences. Second, although the natural spectacle of the Qiantang River Tide can be viewed every day, there is a difference between high-and low-tide days in each month. Finally, the study inevitably had errors in the statistical caliber of travel costs and tourists' willingness to pay. Social, environmental, and other sudden events will have a greater impact on the economic value of a soundscape, such as COVID-19. The assessment of the economic value of the soundscape is constantly in dynamic change.
There still exist some interesting avenues for further investigation. First, the accuracy of soundscape separation and value assessment needs to be further improved. Methods such as choice experiments can be considered to try to obtain tourists' willingness to pay by comparing the different attributes of research objects with one another, so as to minimize the influence of the external environment. Second, in order to further explore the impact of the quality of a soundscape on its economic value in different periods of time, the next study can consider comparing the results of high-and low-tide day visitor data to promote the dynamic assessment of the value of soundscapes. Finally, future researchers can try to use a variety of acoustic methods, such as soundwalk, in order to achieve a threefold correlation study between economic value attributes and physical acoustic attributes, as well as tourists' perception. Through the above methods, a dynamic soundscape map can be drawn to better guide the sustainable development of the scenic spots and the practice of soundscape planning.   What is the importance to you of the three most impressive landscapes above? Please rank them two by two.

Extremely Unimportant
Unimportant Equivalent More Important Extremely Important Landscape 1 than Landscape 2 Landscape 1 than Landscape 3 Landscape 2 than Landscape 3 10. What senses do you use when you enjoy the Yanguan First-line Tide? (multiple selection) A. Vision B. Hearing C. Tactile D. Smell E. Taste F. Others, please specify. 11. Please write the number of the three senses you think are most used. (A-E) Sensory 1; Sensory 2; Sensory 3. 12. What is the importance to you of the three senses most used above? Please rank them two by two.

Extremely Unimportant
Unimportant Equivalent More Important Extremely Important Sensory 1 than Sensory 2 Sensory 1 than Sensory 3 Sensory 2 than Sensory 3 Total transportation costs: ; Total accommodation costs: ; Total food and beverage costs: ; Other costs such as tickets, shopping, etc.: . □ Through travel agency: Fees paid to travel agency: ; Other additional costs such as tickets and souvenirs: . 18. Are you willing to pay a fee to protect the ecological environment of the Qiantang River Tide and perpetuate its existence? □ Unwilling □ Willing; If you wish, please type √ after the amount of money you will definitely pay and × after the amount of money you will definitely not pay.