TIMELINE 1-km AVHRR basis parameters: reflectance, clouds, LST

Kurzfassung

In order to re-process DLRs 1km AVHRR data archive to different geophysical and descriptive parameters of the land surface and the atmosphere, a series of scientific data processors are being developed in the framework of the TIMELINE project. The archive of DLR ranges back to the 80ies. The data is preprocessed to L1b and harmonized for sensor effects. The detection of clouds and the processing of cloud properties are done using APOLLO_NG (APOLLO_NextGeneration), which is a probabilistic interpretation of the classical APOLLO scheme, building on its physical principles. Cloud detection is expressed as cloud probability for each satellite pixel. Furthermore, the probabilistic approach of APOLLO_NG allows the retrieval of cloud properties (optical depth, effective radius, cloud top temperature and cloud water path) along with their uncertainties. The radiative transfer solution is approximated by a two-stream approach, which allows the online calculation of the radiative transfer. Further processing of the visible bands includes the TAC (TIMELINE Atmospheric Correction) step, in which atmospheric correction is done on the basis of LUTs. BRDF is corrected using a temporal moving window approach. The thermal bands of the L1b product are used for LST estimation with SurfTemp. Its development included the selection of statistical procedures suitable for time series processing. In a round robin approach, the selected algorithms are tested on the basis of a large number of TOA radiance/LST pairs, which were generated using a radiative transfer model and the SeeBorV5 profile database. The algorithm comparison includes measures of precision, as well as the sensitivity of a method to the accuracy of its input data. Besides the implementation into SurfTemp, first cross-validation results between the AVHRR LST and MODIS LST are shown.