A first attempt to build an ASTER global mosaic in pseudo-true color

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra satellite, which was launched in 1999, is an optical sensor that can observe the wavelength range from visible to thermal. This instrument has been developed by the Japanese Ministry of Economy, Trade, and Industry (METI), and has high spatial resolution, four visible and near-infrared bands at 15m, six shortwave infrared bands at 30m, and five thermal infrared bands at 90m. As ASTER doesn't have blue visible band, we developed an algorithm to estimate the ASTER blue reflectance using data observed by ASTER and Moderate Resolution Imaging Spectroradiometer (MODIS) on the same platform, Terra. After atmospheric corrections, the ASTER pseudo-blue band was constructed from an artificial neural network (ANN), making it possible to generate ASTER granules in true color composite. These processed ASTER imageries are distributed by the AIST MADAS system as one of ASTER-VA products.

On the other hand, global cloud-free mosaic of true color satellite imageries can be used as various base-maps for both public and scientific uses. We attempted to generate a 15m cloud-free global mosaic using the processed ASTER images. Moreover, for the few ASTER cloudy or no observation areas we implemented Landsat-7 ETM+. We used Landsat-7 ETM+ Mosaic product processed by NASA/JPL CalTech, which is derived from GeoCover2000. To correct the seasonal effects and to build a homogeneous mosaic the ASTER and LANDSAT reflectances were adjusted to a common reference target. We successfully produced a 15m global and seamless mosaic that will be freely distributed to the public on the web site in future (https://gbank.gsj.jp/madas/?lang=en).