Abstract
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) program delivered the GMI Instrument to Goddard Space Flight Center early 2012. Currently, the GMI instrument is undergoing observatory-level integration and test. Goddard Space Flight Center plans to launch the GMI in 2014 aboard the GPM spacecraft with the Dual-frequency Precipitation Radar, affording better correlation of active and passive measurement techniques. The GMI will fly in a 65 degree inclination orbit and is intended to become the calibration standard for radiometer precipitation measurements.
The GMI Instrument calibration design includes unique features to limit calibration errors that have been observed with previous radiometers. The design includes the following features: 1) geometrically blocking of solar intrusion into the hot load, 2) containment of the hot load in a tray with known temperature in order to estimate and remove induced gradients into the hot load, 3) a dual calibration design using both a standard hot and cold source and noise diodes, 4) and the use of a proven main reflector coating technology to ensure high reflectance.
Calibration performance based on ground calibration data taken in thermal vacuum tests together with other component tests and analyses are presented. The main measurements taken to demonstrate calibration performance include: 1) thermal vacuum measurements of non-linearity and radiometric stability, 2) beam pattern measurements including modeled backlobe estimates for the main beam and cold sky beams, 3) validated thermal model predictions of hot load thermal gradient performance, 4) and demonstrated high reflector coating conductance. The calibration design meets the GMI calibration uncertainty requirements.
Global Precipitation Measurement Microwave Imager (GMI) Pre-flight Calibration Performance
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) program delivered the GMI Instrument to Goddard Space Flight Center early 2012. Currently, the GMI instrument is undergoing observatory-level integration and test. Goddard Space Flight Center plans to launch the GMI in 2014 aboard the GPM spacecraft with the Dual-frequency Precipitation Radar, affording better correlation of active and passive measurement techniques. The GMI will fly in a 65 degree inclination orbit and is intended to become the calibration standard for radiometer precipitation measurements.
The GMI Instrument calibration design includes unique features to limit calibration errors that have been observed with previous radiometers. The design includes the following features: 1) geometrically blocking of solar intrusion into the hot load, 2) containment of the hot load in a tray with known temperature in order to estimate and remove induced gradients into the hot load, 3) a dual calibration design using both a standard hot and cold source and noise diodes, 4) and the use of a proven main reflector coating technology to ensure high reflectance.
Calibration performance based on ground calibration data taken in thermal vacuum tests together with other component tests and analyses are presented. The main measurements taken to demonstrate calibration performance include: 1) thermal vacuum measurements of non-linearity and radiometric stability, 2) beam pattern measurements including modeled backlobe estimates for the main beam and cold sky beams, 3) validated thermal model predictions of hot load thermal gradient performance, 4) and demonstrated high reflector coating conductance. The calibration design meets the GMI calibration uncertainty requirements.