The Global Precipitation Measurement (GPM) mission is an international satellite mission that uses measurements from an advanced radar/radiometer system on a core observatory as reference standards to unify and advance precipitation estimates made by a constellation of research and operational microwave sensors. The GPM core observatory was launched on February 27, 2014 at 18:37 UT in a 65 • inclination nonsun-synchronous orbit. GPM focuses on precipitation as a key component of the Earth's water and energy cycle, and has the capability to provide near-real-time observations for tracking severe weather events, monitoring freshwater resources, and other societal applications. The GPM microwave imager (GMI) on the core observatory provides the direct link to the constellation radiometer sensors, which fly mainly in polar orbits. The GMI sensitivity, accuracy, and stability play a crucial role in unifying the measurements from the GPM constellation of satellites. The instrument has exhibited highly stable operations through the duration of the calibration/validation period. This paper provides an overview of the GMI instrument and a report of early on-orbit commissioning activities. It discusses the on-orbit radiometric sensitivity, absolute calibration accuracy, and stability for each radiometric channel.Index Terms-Calibration accuracy, passive microwave remote sensing, radiometric sensitivity.
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) instrument was launched onboard the GPM core spacecraft in February 2014. The instrument has exhibited highly stable operations through the duration of the calibration/ validation period. This paper provides an overview of the GMI instrument and a report of early onorbit commissioning activities. It discusses the on-orbit radiometric sensitivity and stability for each channel, hot load performance, noise diode stability and early indicators of absolute calibration performance.
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) Instrument is being developed by Ball Aerospace and Technology Corporation (BATC) for the GPM program at NASA Goddard.The Global Precipitation Measurement (GPM) mission is an international effort managed by the National Aeronautics and Space Administration (t.JASA) to improve climate, weather, and hydro-meteorological predictions through more accurate and more frequent precipitation measurements. The GPM Microwave Imager (GMI) will be used to make calibrated, radiometric measurements from space at multiple microwave frequencies and polarizations. GMI will be placed on the GPM Core Spacecraft together with the Dualfrequency Precipitation Radar (DPR). The DPR is two-frequency precipitation measurement radar, which will operate in the Ku-band and Ka-band of the microwave spectrum. The Core Spacecraft will make radiometric and radar measurements of clouds and precipitation and will be the central element ofGPM's space segment. The data products from GPM will provide information concerning global precipitation on a frequent, near-global basis to meteorologists and scientists making weather forecasts and performing research on the global energy and water cycle, precipitation, hydrology, and related disciplines. In addition, radiometric measurements from GMI and radar measurements from the DPR will be used together to develop a retrieval transfer standard for the purpose of calibrating precipitation retrieval algorithms. This calibration standard will establish a reference against which other retrieval algorithms using only microwave radiometers (and without the benefit ofthe DPR) on other satellites in the GPM constellation will be compared.https://ntrs.nasa.gov/search
The Global Precipitation Measurement (GPM) Microwave Imager (GMI) was built and tested by Ball Aerospace and Technologies Corporation (Ball) under a contract with the GPM program at the NASA Goddard Space Flight Center. Ball has supported the initial on-orbit operations to verify calibration performance and provide a final set of operational calibration algorithms. The GMI instrument was launched onboard the GPM spacecraft on February 28th, 2014. GMI was turned on and completed all deployments March 1st, 2014. Spin up and the start of science operations proceeded on March 4th, 2014. GMI has operated nearly continuously since then and has completed a year of successful operation on-orbit. This paper presents the on-orbit performance of the instrument and the results from the calibration activities.Index Terms-microwave radiometer, calibration MISSION AND INSTRUMENT OVERVIEWThe GPM Mission is an international effort managed by NASA to improve climate, weather, and hydrometeorological predictions through more accurate and more frequent precipitation measurements [1]. The GPM spacecraft orbits at 407km carrying both the GMI and the Dual-frequency Precipitation Radar (DPR). The GMI makes calibrated passive radiometric measurements at multiple microwave frequencies to infer precipitation. The GMI is the calibration standard for the GPM constellation. The GPM spacecraft flies in a mid-latitude orbit that crosses the orbits of other polar-orbit radiometers.Using coincident measurements, the calibration of GMI is transferred to the other radiometers in the GPM constellation.The GMI instrument consists of 13 radiometric channels from 10.65 GHz to 183.31 GHz (see Table I), providing accurate measurement of precipitation and multiple other environmental parameters. The GMI has a deployable antenna making it relatively compact for the 1.2 meter aperture size. For the GPM orbit, the GMI antenna provides 25 km native resolution at the lowest frequency and up to 5 km resolution at the higher frequencies. As the GPM calibration standard, multiple calibration enhancements are designed into the GMI to improve calibration accuracy over heritage systems. The enhancements include tight shrouding around the hot load to keep out the sun, noise diodes on the 7 low frequency channels to provide a dual calibration system, and a proven robust reflective coating for the antenna. The state-of-the-art receiver subsystem built by ITT Exelis provides low noise figures and very good stability for excellent radiometric performance [2]. ON-ORBIT PERFORMANCEGMI performance over the first 6 months is described in [2][3][4]. The instrument has now operated for more than a year. Since launch, the spacecraft has gone through 4 complete beta angle cycles exposing the instrument to the entire range of orbital conditions multiple times. The instrument continues to meet or exceed all performance requirements. Key operational parameters like spin rate, spin motor drive current, disturbance torque and consumed power all continue with stable performance meetin...
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