Solar radiation enters the Earth's atmosphere with a portion being scattered by clouds and aerosols.

Processing, archiving and distributing Earth science data
at the NASA Langley Research Center

Where do I find the latitude and longitude of an L1B2 SOM grid location? How do I geolocate?

This process is described in the MISR Data Product Specifications, Appendix A. There are two methods for doing this:

  1. Look up the Lat/Lon of the corresponding block, line, sample in the Ancillary Geographic Product (AGP) data sets.

    MISR geolocation information is located in the MISR Ancillary Geographic Product (AGP) files. The fields "GeoLatitude" and "GeoLongitude" contain the desired information. These values are stored on the "Standard" (1.1 km) grid of the AGP; you may need to interpolate or extrapolate if the parameter you are working with is on a different grid. Latitudes are geodetic, and longitudes are relative to the Greenwich meridian, positive to the east and negative to the west.

    You will need to obtain the AGP file that corresponds to the path of the data you are trying to geolocate. The path is given in the MISR data file name using the format _Pxxx_ where xxx is the path number (1-233).

  2. Mathematically convert the SOM block, line, and sample (pixel) to latitude and longitude. This is a two-step process. Algorithms are provided in the DPS Appendix A.

    • Convert(block, line, sample) <=> SOM(x,y)
      Requires several metadata values from the data file and some arithmetic
    • Convert SOM(x,y) <=> Lat/Lon
      Requires use of GCTP (General Coordinate Transformation Package) map projection coordinate conversion library in HDF-EOS distribution or some other software that incorporates GCTP, such as IDL.