GPM Geolocation Toolkit Algorithm Theoretical Basis Document (ATBD)
This document describes the algorithms for the Geolocation Toolkit (GeoTK) for the Global Precipitation Measurement (GPM) Mission. The core part of the algorithm uses input orbit ephemeris, spacecraft attitude, and instrument pointing data to compute each pixel latitude and longitude viewed, along with ancillary data such as zenith/incidence and Sun angle data. These calculations are implemented in the GeoTK software subroutines, which will be used for Level 1B (L1B) algorithms for GPM. The details of this software structure, inputs and outputs, are documented in the PPS Geolocation Toolkit Architecture and Design Specification Document (Bilanow, 2012). In addition, this document provides a description of how the sensor alignment angles for input to the algorithm are defined, and how these angles may be adjusted based on misalignments observed after launch.