Fine Resolution Air Quality Monitoring from a Small Satellite: CHRIS/PROBA
Abstract
:1. Introduction
2. Images
3. Methodology
3.1. Image pre-processing
3.2. Estimation of Surface Reflectance (Lsurf)
- where TOA490 =reflectance at TOA
- ρ490 =reflectance by Aerosol scattering
- T0 · TS =downward and upward transmittance
- Lsurf490 =surface reflectance
- S = hemispheric albedo
3.3. Validation
- (i)
- comparison of AOT values with sunphotometer data from the AERONET station and two handheld Microtops II sunphotometers [23] deployed in rural forest and an urban forest island at the image time. (The rural forest training areas were located in lowland areas and at least 100 m from the urban edge to avoid the adjacency effect from bright urban surfaces). Since the objective of the study is to detect detailed spatial variation, and with the AERONET site located 1.5 km beyond the image area, the AERONET values are only used as an approximate reference. AERONET values were interpolated to correspond with the CHRIS bands
- (ii)
- comparison with four air quality stations within the image area, and
- (iii)
- visual interpretation using a Digital Elevation Model (DEM).
4. Results
4.1. Comparison with ground sunphotometers
4.2. Comparison with ground air pollution data
4.3. Visual interpretations
5. Discussion
- (i)
- the assumption of linearity when converting TOA1019 to Lsurf1019 by deduction of the difference between them as observed by field radiometer (Figure 2). The deduction of approximately 10% of TOA1019 ie. 3.3% to reduce TOA1019 to Lsurf1019 appears effective since it is likely that the 10% relationship is linear for the larger particle sizes to which the 10% difference applies. An estimate of the error can be given, thus an error in Lsurf1019 of 1 s.d. ie. 1.46% converted to AOT would produce an error in Lsurf490 of 0.06% and in Lsurf661 of 0.16%, thus an AOT error of 0.06 in blue, and 0.04 in red. This is comparable with MODIS AOT retrievals where the error in Lsurf due to the assumption of surface reflectance for the SWIR 2,100 nm band is given by Kaufman et al. [26] as +/-0.6% for blue and red bands, translating to an error in AOT of +/-0.06. Thus the error in the derivation of Lsurf in this project is reasonable
- (ii)
- variability in the relationship between CHRIS Lsurf1019 and Lsurf for blue and red bands, with correlation coefficients of 0.86 and 0.79 respectively. However these compare reasonably with the 0.75 and 0.93, observed for MODIS 2,100 nm band correlated with the blue and red bands [15]
- (iii)
- assumptions in the aerosol model used which Chu et al. [27] suggested can range from 0-20%, but since an aerosol model devised for Hong Kong was used, this error is likely to be considerably reduced
- (iv)
- interpolation between AERONET and CHRIS bands which may account for 0-10% depending on the aerosol type [21].
6. Conclusions
Acknowledgments
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Urban Forest | Band 2: 490 nm | Band 7: 661 nm | ||||
---|---|---|---|---|---|---|
Dec-05 | Feb-06 | Sept-06 | Dec-05 | Feb-06 | Sept-06 | |
AERONET | - | 0.55 | 0.69 | - | 0.38 | 0.44 |
Microtops II | - | - | 0.72 | - | - | 0.47 |
Image AOT | 0.50-0.62 | 0.63-0.69 | 0.71-0.75 | 0.24-0.28 | 0.4-0.47 | 0.32-0.41 |
Rural Forest | Band 2: 490 nm | Band 7: 661 nm | ||||
Dec-05 | Feb-06 | Sept-06 | Dec-05 | Feb-06 | Sept-06 | |
AERONET | - | 0.55 | 0.69 | - | 0.38 | 0.44 |
Microtops II | - | - | 0.67 | - | - | 0.46 |
Image AOT | 0.43-0.50 | 0.52-0.6 | 0.63-0.69 | 0.21-0.26 | 0.25-0.4 | 0.24-0.39 |
TOA | Lsurf | Path Reflectance | MSR (mean) | |||||||
---|---|---|---|---|---|---|---|---|---|---|
Dec-05 | Feb -06 | Sep -06 | Dec-05 | Feb -06 | Sep -06 | Dec-05 | Feb -06 | Sep -06 | ||
B2 490nm | 10.4 | 11.3 | 11.5 | 1.4 | 1.5 | 2.0 | 9.0 | 9.8 | 9.3 | 1.64 |
B18 1019nm | 28 | 30.8 | 31.6 | 26.5 |
© 2008 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the CreativeCommons Attribution license (http://creativecommons.org/licenses/by/3.0/).
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Nichol, J.E.; Wong, M.S.; Chan, Y.Y. Fine Resolution Air Quality Monitoring from a Small Satellite: CHRIS/PROBA. Sensors 2008, 8, 7581-7595. https://doi.org/10.3390/s8127581
Nichol JE, Wong MS, Chan YY. Fine Resolution Air Quality Monitoring from a Small Satellite: CHRIS/PROBA. Sensors. 2008; 8(12):7581-7595. https://doi.org/10.3390/s8127581
Chicago/Turabian StyleNichol, Janet E., Man Sing Wong, and Yuk Ying Chan. 2008. "Fine Resolution Air Quality Monitoring from a Small Satellite: CHRIS/PROBA" Sensors 8, no. 12: 7581-7595. https://doi.org/10.3390/s8127581
APA StyleNichol, J. E., Wong, M. S., & Chan, Y. Y. (2008). Fine Resolution Air Quality Monitoring from a Small Satellite: CHRIS/PROBA. Sensors, 8(12), 7581-7595. https://doi.org/10.3390/s8127581