Microwave Radiometer (MWR) Beam-Pointing for the Aquarius/SAC-D Mission
[11-Nov-2014] Clymer, B., May, C., Schneidar, L., Madero, F., Labanda, M., Jacob, M., and Jones, L.
Presented at the 2014 Aquarius/SAC-D Science Team Meeting
This poster concerns the on-orbit validation of the antenna beam pointing and corresponding instantaneous field of view (IFOV) earth location for the CONAE Microwave Radiometer (MWR). The MWR is a three-channel radiometer operating at 23.8 GHz (H-Pol) and 36.5 GHz (V- and H-Pol), which has two multi-beam parabolic reflector antennas in a pushbroom configuration, with eight beams per frequency (36.5 GHz looking forward and 23.8 GHz looking aft producing 24 simultaneous beams). The scene brightness temperature is dependent upon the earth incidence angle, and MWR retrieval algorithms require good IFOV collocation between channels. Thus, knowledge of the MWR antenna beam footprint geolocation is important to mission success.
As a result, this poster presents results of an on-orbit validation of the MWR antenna beam pointing and comparison with observed and calculated (geometric) MWR IFOV centers. This procedure compares CONAE-calculated IFOV centers at land/water crossings against high-resolution coastline maps. MWR IFOV locations versus time are computed from knowledge of the satellite's ephemeris, attitude (roll, pitch and yaw) and a priori measurements of antenna gain pattern boresight directions and mounting geometry.
Previous conical scanning microwave radiometer missions (e.g., SSMI and WindSat) have utilized the observation of rapid change in T_B at land/water boundaries to determine the antenna beam-pointing location. In this paper, results of an algorithm to quantify the geolocation error of MWR beam center is presented, based upon two-dimensional convolution between each beam's gain pattern and land-water transition based upon a 1 km coastline map. The analysis procedures have been applied to on-orbit datasets that represent selected land-water boundaries bearing specific desirable criteria. The goal of this research is to estimate the satellite radiometer beam-pointing error and thereby to improve the geolocation (latitude and longitude) given in the MWR level-1 science data. Examples of colocation comparisons are presented for selected "super sites" with favorable geometry.