| Paper: | TH-A1.1 |
| Session: | Applications of Radiometry I |
| Time: | Thursday, March 29, 09:00 - 10:20 |
| Presentation: |
Poster
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| Topic: |
Theory, physical principles and electromagnetic models: |
| Title: |
Global Precipitation Measurement (GPM) Microwave Imager (GMI) After Four Years On-orbit |
| Authors: |
David Draper; Ball Aerospace & Technologies Corp. | | |
| | David Newell; Ball Aerospace & Technologies Corp. | | |
| Abstract: |
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) was launched aboard the GPM Core Observatory in February 2014. Flying in a 65 degree inclination orbit, the GMI is the calibration standard for radiometer precipitation measurements made by the GPM constellation instruments. The GMI continues to operate nominally with very stable radiometric output on all 13 channels. The radiometric sensitivity in terms of Noise Equivalent Delta Temperature (NEDT) has remained nearly constant over the first four years of operation.
The GMI employs a unique dual calibration system. Like other scanning microwave imagers, the GMI provides primary calibration using a hot load blackbody and cold sky view. The GMI also employs a secondary calibration system with noise sources on the lower frequency channels, providing four calibration points rather than two. The dual calibration provides a method of trending the GMI calibration performance including the hot load performance, noise diode excess temperature drift, and non-linearity.
The GMI hot load was designed with very tight shrouding to eliminate intrusion from the sun onto its RF-emissive surface. The GMI hot load continues to exhibit very stable performance with low thermal gradients. The instrument has undergone multiple solar beta angle cycles with no solar intrusion onto the hot load surface.
The GMI noise diodes have experienced minor drift except the 10 GHz V-pol noise diode which has exhibited somewhat erratic behavior. Since the noise diodes are not used for the primary calibration, this behavior does not affect the GMI radiometric performance, but does provide insight into the types of errors that might be seen for radiometers that only have noise diodes as the primary calibration source.
The GMI cold sky view algorithm utilizes a flagging routine to identify Radio Frequency Interference (RFI) from Geosynchronous Satellites that may intrude into the cold sky view. The RFI flagging routine is shown to eliminate the effects of RFI to below the ability to detect within the calibrated output.
Radio Frequency Interference continues to persist in the 10 and 18 GHz channels in the Earth View from both ground-based and satellite-based sources. The non-linearity of the channels with noise diodes continues to be exceptionally stable.
The GMI continues to operate with excellent stability, and likely will continue for years to come.
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