How can I read AMSR-E Level-2 Soil Moisture Data?
HDF-EOS defines three different data models – point, swath, and grid – each of which is constructed using standard HDF data types. While all other AMSR-E Level-2B products use the swath data model, the soil moisture product is unique in using the point data model. By using the point data model, each observation in the swath may be mapped to a location in the projected grid that is used for the Level-3 data.
HDF-EOS data files are supported by the HDF-EOS library, which allows data products to be created and manipulated in ways appropriate to each HDF-EOS data type without regard to the actual HDF objects underlying them. Thus, it is recommended that the HDF-EOS library be used for reading all HDF-EOS files. However, users who do not wish to download and install the HDF-EOS library may use the HDF library to read any HDF-EOS file. In addition, many commercial software packages such as IDL, ERDAS IMAGINE, and MATLAB have the HDF library built in, as well as the HDF-EOS library in the case of IDL.
To read AMSR-E Level-2B Soil Moisture data, the user must be aware of how the point data model is implemented. Specifically, the point data model uses the Vdata HDF object instead of the SDS data object to hold data. If using the HDF library as opposed to the HDF-EOS library, the routine needed is VSread. If using IDL, the EOS_PT_OPEN and related functions allow you access to the HDF-EOS specific interface for the point data type. The command-line utility HDP can also be used to dump the Vdata with the function dumpvd.
The HDF-EOS library is available for most common operating systems at: http://newsroom.gsfc.nasa.gov/sdptoolkit/toolkit.html
The HDF Reference Manual can be found at: ftp://ftp.hdfgroup.org/HDF/prev-Documentation/HDF4.2r1/HDF42r1_RefMan.pdf