TRMM Microwave Imager (TMI) Alignment and Along-Scan Bias Corrections

The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) dataset released by the Precipitation Processing System (PPS) has been updated to a final version following the decommissioning of the TRMM satellite in April 2015. The updates are based on increased knowledge of radiometer calibration and sensor performance issues. In particular, the Global Precipitation Measurement (GPM) Microwave Imager (GMI) is used as a model for many of the TMI updates. This paper discusses two aspects of the TMI data product that have been reanalyzed and updated: alignment and along-scan bias corrections. The TMI's pointing accuracy is significantly improved over prior PPS versions, which used at-launch alignment values.A TMI instrument mounting offset is discovered as well as new alignment offsets for the two TMI feedhorns. The original TMI along-scan antenna temperature bias correction is found to be generally accurate over ocean, but a scene temperature-dependent correction is needed to account for edge-of-scan obstruction. These updates are incorporated into the final TMI data version, improving the quality of the data product and ensuring accurate geophysical parameters can be derived from TMI

The NASA CYGNSS SmallSat Constellation

The NASA Cyclone Global Navigation Satellite System (CYGNSS) is a constellation of eight microsatellites in low earth orbit at ~525 km altitude and 35 deg inclination. CYGNSS was launched in December 2016 for a planned 2 year mission and 7 of the 8 spacecraft continue to operatue nominally as of May 2023. Each microsatellites carries a bistatic radar receiver to measure reflected GPS signals from the Earth surface. The measurements can be converted to surface wind speed and latent and sensible heat flux over the ocean, and to surface soil moisture and wetland extent over land. Measurements penetrate through all levels of precipitation as well as moderate to heavy vegetation due to the low microwave frequency used by GPS. The number of satellites in the constellation results in sub-daily refresh rates which supports imaging of short time scale weather events such as hurricane rapid intensification, flood inundation dynamics, and sudden soil saturation after major rain events. CYGNSS satellites uses a single string design architecture to reduce the complexity and recurring cost of each unit. Mission redundancy is obtained at the constellation level. Data products are produced by combining measurements from all satellites in such a way that the sampling requirements can be met using only a subset of the satellites. Constellation-level redundancy also permits individual satellites to be switched from their nominal science data taking mode to various engineering test and calibration modes while the overall mission is still able to meet its science requirements

TRMM Microwave Imager (TMI) Updates for Final Data Version Release

The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) dataset released by the Precipitation Processing System (PPS) will be updated to a final version within the next year. These updates are based on increased knowledge in recent years of radiometer calibration and sensor performance issues. In particular, the Global Precipitation Measurement (GPM) Microwave Imager (GMI) is used as a model for many of the TMI version updates. This paper discusses four aspects of the TMI data product that will be improved: spacecraft attitude, calibration and quality control, along-scan bias corrections, and sensor pointing accuracy. These updates will be incorporated into the final TMI data version, improving the quality of the data product and ensuring accurate geophysical parameters can be derived from TMI

SATELLITE ATTITUDE ANALYSIS USING THE VICARIOUS COLD CALIBRATION METHOD FOR MICROWAVE RADIOMETERS

ABSTRACT A method for estimating the pitch and roll errors of a satellite with an onboard conical scanning microwave radiometer is described. The method makes use of the vicarious cold calibration algorithm which derives a stable cold brightness temperature (TB) over ocean. This cold TB is sensitive to the Earth Incidence Angle (EIA) of the radiometer. Given no pitch or roll errors, the EIA can be modeled as a function of the Earth radius and altitude of the satellite. Deviation from this EIA can then be used to estimate the pitch and roll errors. The pitch/roll algorithm is applied to the current spaceborne microwave radiometer WindSat to show its performance, and the results are compared to the derived pitch and roll of WindSat that are found using a different attitude analysis method

Vicarious Calibration of Global Precipitation Measurement Microwave Radiometers

The vicarious cold calibration method of Ruf has been used to assess the calibration of the TMI, WindSat, SSM/I F13 and SSM/I F14 microwave radiometers using data from the GPM Inter-Calibration Working Group. Significant scan position dependent biases are seen for TMI (as large as 1 K) and for WindSat (as large as 5 K) – scan position dependent biases in SSM/I data were removed prior to processing. These biases are thought to be due to obstructions in the edge of scan field of view from the given instrument and its spacecraft. WindSat vertically polarized data also show a linear decrease in vicarious cold calibration brightness temperatures with scan position. SSM/I F13 and F14 vicarious cold brightness temperatures differ by an amount consistent with a ~.2 ° offset in their relative Earth incidence angles

Thin Fisher Zeroes

Biskup et al. [Phys. Rev. Lett. 84 (2000) 4794] have recently suggested that the loci of partition function zeroes can profitably be regarded as phase boundaries in the complex temperature or field planes. We obtain the Fisher zeroes for Ising and Potts models on non-planar (``thin'') regular random graphs using this approach, and note that the locus of Fisher zeroes on a Bethe lattice is identical to the corresponding random graph. Since the number of states appears as a parameter in the Potts solution the limiting locus of chromatic zeroes is also accessible.Comment: 10 pages, 4 figure

Interferometric Synthetic Aperture Microwave Radiometers : an Overview

This paper describes 1) the progress of the work of the IEEE Geoscience and Remote Sensing Society (GRSS) Instrumentation and Future Technologies Technical Committee (IFT-TC) Microwave Radiometer Working Group and 2) an overview of the development of interferometric synthetic aperture microwave radiometers as an introduction to a dedicated session

A Consensus Calibration Based On Tmi And Windsat

The Global Precipitation Measurement (GPM) mission requires a high degree of consistency among the microwave radiometers in the constellation which, in turn, demands a standard against which all the sensors can be compared. Ultimately this standard will be the GPM Microwave Imager, but for the present the TRMM Microwave Imager (TMI) fills this need. Since its calibration leaves much to be desired, a refinement using Windsat has been developed. This article defines the Consensus Calibration 1.1 which is applied to the TMI. In turn the TMI serves as a transfer standard to other satellite radiometers. © 2011 IEEE

Intercalibrating The Gpm Constellation Using The Gpm Microwave Imager (Gmi)

A constellation of disparate radiometers is inherent to the Global Precipitation Measurement (GPM) mission concept. The task of the Intersatellite Calibration Working group is to generate adjustments to make the measurements of all these radiometers physically consistent. A key role of the GPM Microwave Imager (GMI) on the GPM Core satellite is to serve as a transfer standard among the constellation radiometers. The TRMM Microwave Imager (TMI) has served this role during the development phase and for interim corrections early in the GPM mission. The stability of GMI appears to be very good and a physically based calibration has been generated that appears to be accurate at the 1K level or better