Validation of the MODIS reflectance product under UK conditions

Khavarian Nehzak, Hassan, Atkinson, P.M., Milton, E.J. and Stewart, J.B. (2013) Validation of the MODIS reflectance product under UK conditions. International Journal of Remote Sensing, 34 (20), 7376-7399. (doi:10.1080/01431161.2013.82036).

Abstract

Surface reflectance obtained from remote sensing data is the main input to almost all remote sensing applications. The availability and special characteristics of MODIS products have led to their use worldwide. Validation of the MODIS reflectance product is then crucial to provide information on uncertainty in the reflectance data, and in other MODIS products and in the applied surface-atmosphere models. Airborne CASI and SPOT data, collected during the NCAVEO 2006 Field Campaign, were applied to validate daily MODIS reflectance data over a site in southern England. The difference in the view geometry of at-nadir CASI and SPOT data and off-nadir MODIS data was dealt with using a semi-empirical bidirectional reflectance distribution function (BRDF) model. The validation results showed that for our particular study site, the absolute errors in the MODIS reflectance product were too large to allow the albedo data to be used directly in climate models. The errors were mainly related to the uncertainties in the MODIS atmospheric variables, the BRDF model, and undetected clouds and cloud shadows. More generally, the study highlights the extreme difficulty of achieving pixel-level validation of coarse spatial resolution satellite sensor data in an environment in which the atmosphere is constantly changing, and in which the landscape is characterised by high space-time heterogeneity

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Contributors

Author: P.M. Atkinson

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