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Open AccessArticle

Increasing the Number of Sea Surface Reflected Signals Received by GNSS-Reflectometry Altimetry Satellite Using the Nadir Antenna Observation Capability Optimization Method

by Zongqiang Liu 1,2,†, Wei Zheng 1,2,3,4,5,6,7,*,†, Fan Wu 2,†, Guohua Kang 1, Zhaowei Li 2, Qingqing Wang 1,2 and Zhen Cui 8
1
School of Astronautics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
2
Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
3
School of Data Science, Taiyuan University of Technology, Jinzhong 030600, China
4
School of Geomatics, Liaoning Technical University, Fuxin 123000, China
5
College of Aeronautics and Astronautics, University of Electronic Science and Technology of China, Chengdu 611731, China
6
School of Surveying and Landing Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China
7
School of Instrumental Science and Engineering, Southeast University, Nanjing 210096, China
8
Xian Institute of Space Radio Technology, China Academy of Space Technology, Xian 710100, China
*
Author to whom correspondence should be addressed.
Those authors contributed equally to this paper.
Remote Sens. 2019, 11(21), 2473; https://doi.org/10.3390/rs11212473
Received: 12 September 2019 / Revised: 21 October 2019 / Accepted: 21 October 2019 / Published: 23 October 2019
(This article belongs to the Special Issue Global Navigation Satellite Systems for Earth Observing System)
High spatial resolution Global Navigation Satellite System-Reflectometry (GNSS-R) sea surface altimetry is of great significance for extracting precise information from sea surface topography. The nadir antenna is one of the key payloads for the GNSS-R altimetry satellite to capture and track the sea surface GNSS reflected signal. The observation capability of the nadir antenna directly determines the number of received reflected signals, which, in turn, affects the spatial resolution of the GNSS-R altimetry. The parameters affecting the ability of the nadir antenna to receive the reflected signal mainly include antenna gain, half-power beam width (HPBW), and pointing angle. Thus far, there are rarely studies on the observation capability of GNSS-R satellite nadir antenna. The design of operational satellite antenna does not fully combine the above three parameters to optimize the design of GNSS-R nadir antenna. Therefore, it is necessary to establish a GNSS-R spaceborne nadir antenna observation capability optimization method. This is the key to improving the number of sea surface reflected signals received by the GNSS-R altimeter satellites, thereby increasing the spatial resolution of the altimetry. This paper has carried out the following research on this. Firstly, based on the GNSS-R geometric relationship and signal processing theory, the nadir antenna signal-to-noise ratio model (NASNRM) with the gain and the elevation angle at the specular point (SP) as the main parameters is established. The accuracy of the model was verified using TechDemoSat-1 (TDS-1) observations. Secondly, based on the theory of electromagnetic scattering, considering the influence of HPBW and pointing angle on the antenna footprint size, a specular point filtering algorithm (SPFA) is proposed. Combined with the results obtained by NASNRM, the number of available specular points (SPs) is counted. The results show that as the antenna gain and the nadir-pointing angle increase, the number of SPs can reach a peak and then gradually decrease. Thirdly, combined with NASNRM and SPSA, a nadir antenna observation capability optimization method (NAOCOM) is proposed. The nadir antenna observation capability is characterized through the reflected signal utilization, and the results obtained by the method are used to optimize the combination of nadir antenna parameters. The research shows that when the orbital height of the GNSS-R satellite is 635 km, the optimal combination of nadir antenna parameters is 20.94 dBi for the gain and 32.82 degrees for the nadir-pointing angle, which can increase the observation capability of the TDS-1 satellite nadir antenna by up to 5.38 times. View Full-Text
Keywords: Global Navigation Satellite System-Reflectometry; spaceborne nadir antenna; observation capability optimization; ocean altimetry; sampling spatial resolution; elevation angle; reflected signals utilization; TechDemoSat-1 Global Navigation Satellite System-Reflectometry; spaceborne nadir antenna; observation capability optimization; ocean altimetry; sampling spatial resolution; elevation angle; reflected signals utilization; TechDemoSat-1
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MDPI and ACS Style

Liu, Z.; Zheng, W.; Wu, F.; Kang, G.; Li, Z.; Wang, Q.; Cui, Z. Increasing the Number of Sea Surface Reflected Signals Received by GNSS-Reflectometry Altimetry Satellite Using the Nadir Antenna Observation Capability Optimization Method. Remote Sens. 2019, 11, 2473.

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