Geography Research Works

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End date: 2009Subject: search.filters.subject.Moderate Resolution Imaging Spectroradiometer

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    A Direct Algorithm for Estimating Land Surface Broadband Albedos From MODIS Imagery
    (Institute of Electrical and Electronics Engineers, 2003-01) Liang, Shunlin
    Land surface albedo is a critical variable needed in land surface modeling. The conventional methods for estimating broadband albedos rely on a series of steps in the processing chain, including atmospheric correction, surface angular modeling, and narrowband-to-broadband albedo conversions. Unfortunately, errors associated with each procedure may be accumulated and significantly impact the accuracy of the final albedo products. In an earlier study, we developed a new direct procedure that links the top-of-atmosphere spectral albedos with land surface broadband albedos without performing atmospheric correction and other processes. In this paper, this method is further improved in several aspects and implemented using actual Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Several case studies indicated that this new method can predict land surface broadband albedos very accurately and eliminate aerosol effects effectively. It is very promising for global applications and is particularly suitable for nonvegetated land surfaces. Note that a Lambertian surface has been assumed in the radiative transfer simulation in this paper as a first-order approximation; this assumption can be easily removed as long as a global bidirectional reflectance distribution function climatology is available,
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    Estimation of Systematic Errors of MODIS Thermal Infrared Bands
    (Institute of Electrical and Electronics Engineers, 2006-10) Liang, Shunlin; Liu, Ronggao G.; Liu, Jiyuan Y.
    This letter reports a statistical method to estimate detector-dependent systematic error in Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared (TIR) Bands 20–25 and 27–36. There exist scan-to-scan overlapped pixels in MODIS data. By analyzing a sufficiently large amount of those most overlapped pixels, the systematic error of each detector in the TIR bands can be estimated. The results show that the Aqua MODIS data are generally better than the Terra MODIS data in 160 MODIS TIR detectors. There are no detector-dependent systematic errors in Bands 31 and 32 for both Terra and Aqua MODIS data. The maximum detector errors are 3.00 K in Band 21 of Terra and −8.15 K in that of Aqua for brightness temperatures of more than 250 K.
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    Mapping daily snow/ice shortwave broadband albedo from Moderate Resolution Imaging Spectroradiometer (MODIS): The improved direct retrieval algorithm and validation with Greenland in situ measurement
    (American Geophysical Union, 2005-05-26) Liang, Shunlin; Stroeve, Julienne; Box, Jason E.
    Snow/ice albedo is a critical variable in surface energy balance calculations. The Moderate Resolution Imaging Spectroradiometer (MODIS) data have been used routinely to provide global land surface albedo. The MODIS algorithm includes atmospheric correction, surface reflectance angular modeling, and narrowband to broadband albedo conversion. In an earlier study, a "direct retrieval" methodology was proposed to calculate instantaneous albedo over snow and ice-covered surfaces directly from top-of-atmosphere (TOA) MODIS reflectance data. The method consists of extensive radiative transfer simulations for a variety of atmospheric and surface snow conditions and links the TOA reflectance with surface broadband albedo through regression analysis. Therefore the direct retrieval algorithm implicitly incorporates in a single step all three procedures used in the standard MODIS surface albedo algorithm. This study presents improvements to the retrieval algorithm including validation with in situ measurements distributed over the Greenland ice sheet. Comparison with surface observations demonstrates that the direct retrieval algorithm can produce very accurate daily snow/ice albedo with mean bias of less than 0.02 and residual standard error of 0.04.