Miniaturized microwave radiometers deployed on nanosatellites in Low Earth Orbit are now demonstrating cost-effective weather monitoring capability, with increased temporal and spatial resolution compared to larger weather satellites. MicroMAS-2A is a 3U CubeSat that launched on January 11, 2018 with a 1U 10-channel passive microwave radiometer with channels near 90, 118, 183, and 206 GHz for moisture and temperature profiling and precipitation imaging. The Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission is projected to launch in 2020, and its 1U 12-channel passive microwave radiometer is based on the current CubeSat mission MicroMAS-2A. TROPICS will provide rapid-refresh measurements over the tropics and measure environmental and inner-core conditions for tropical cyclones. In order to effectively use small satellites such as MicroMAS-2A and TROPICS as a weather monitoring platform, calibration must ensure consistency with state of the art measurements, such as the Advanced Technology Microwave Sounder (ATMS), which has a noise equivalent delta temperature (NEDT) at 300 K of 0.5 - 3.0 K. In this work, we present initial analysis from the MicroMAS-2A radiometric bias validation, which compares MicroMAS-2A measured brightness temperatures to simulated brightness temperatures calculated by the Community Radiative Transfer Model (CRTM) using input from GPS radio occultation (GPSRO), radiosonde, and numerical weather prediction (NWP) atmospheric profiles. We also model solar and lunar intrusions for TROPICS, and show that the frequency of intrusions with a scanning payload allows for the novel opportunity of using the solar and lunar intrusions as a calibration source.
As a part of the Joint Polar Satellite System (JPSS, formerly the NPOESS afternoon orbit), the instruments Cross-track
Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) make up the Cross-track Infrared and
Microwave Sounder Suite (CrIMSS). CrIMSS will primarily provide global temperature, moisture, and pressure
profiles and calibrated radiances . In preparation for the NPP launch in 2011, we have ported and tested the
operational CrIMSS Environmental Data Record (EDR) algorithms using both synthetic and proxy data generated from
the IASI, AMSU, MHS data from Metop-A satellite.
Two calibration/validation efforts planned for current and future spaceborne microwave sounding instruments
will be presented. First, the NPOESS Aircraft Sounder Testbed-Microwave (NAST-M) airborne sensor is used
to directly validate the microwave radiometers (AMSU and MHS) on several operational satellites. Comparison
results for underflights of the Aqua, NOAA, and MetOp-A satellites will be shown. Second, a potential approach
will be presented for on-orbit field-of-view (FOV) calibration of the Advanced Technology Microwave Sounder
(ATMS). A variety of proposed spacecraft maneuvers that could facilitate the characterization of the radiometric
boresight of all 22 ATMS channels will be discussed.
Radiance observations from the NAST-M airborne sensor can be used to directly validate the radiometric
performance of spaceborne sensors. NAST-M includes a total of four spectrometers, with three operating near the
oxygen lines at 50-57, 118.75, and 424.76 GHz, and a fourth spectrometer centered on the water vapor absorption
line at 183.31 GHz. All four feedhorns are co-located, have 3-dB (full-width at half-maximum) beamwidths of
7.5° (translating to 2.5-km nominal pixel diameter at nadir incidence), and are directed at a single mirror
that scans cross-track beneath the aircraft with a nominal swath width of 100 km. We will present results
for two recent validation efforts: 1) the Pacific THORpex (THe Observing-system Research and predictability
experiment) Observing System Test (PTOST 2003, Honolulu, HI) and 2) the Joint Airborne IASI Validation
Experiment (JAIVEx 2007, Houston, TX). Radiance differences between the NAST-M sensor and the Advanced
Microwave Sounding Unit (AMSU) and the Microwave Humidity Sensor (MHS) were found to be less than 1K
for most channels. Comparison results for ocean underflights of the Aqua, NOAA, and MetOp-A satellites are
We also present an approach for on-orbit FOV calibration of the ATMS satellite instrument using vicarious
calibration sources with high spatial frequency content (the Earths limb, for example). The antenna beam is
slowly swept across the target of interest and a constrained deconvolution approach is used to recover antenna
pattern anomalies. Various proposed spacecraft maneuvers will be considered, with the intent to illustrate how
each maneuver will help to identify and characterize possible FOV artifacts. Radiative transfer simulations that
quantitatively assess the benefit of each satellite maneuver will also be presented.
We describe a simulation methodology used to develop and validate precipitation retrieval algorithms for current and future
passive microwave sounders with emphasis on the NPOESS (National Polar-orbiting Operational Environmental Satellite
System) sensors. Precipitation algorithms are currently being developed for ATMS, MIS, and NAST-M. ATMS, like AMSU,
will have channels near the oxygen bands throughout 50-60 GHz, the water vapor resonance band at 183.31 GHz, as well as
several window channels. ATMS will offer improvements in radiometric and spatial resolution over the AMSU-A/B and MHS
sensors currently flying on NASA (Aqua), NOAA (POES) and EUMETSAT (MetOp) satellites. The similarity of ATMS to
AMSU-A/B will allow the AMSU-A/B precipitation algorithm developed by Chen and Staelin to be adapted for ATMS, and the
improvements of ATMS over AMSU-A/B suggest that a superior precipitation retrieval algorithm can be developed for ATMS.
Like the Chen and Staelin algorithm for AMSU-A/B, the algorithm for ATMS to be presented will also be based a statisticsbased
approach involving extensive signal processing and neural network estimation in contrast to traditional physics-based
approaches. One potential advantage of a neural-network-based algorithm is computational speed. The main difference in
applying the Chen-Staelin method to ATMS will consist of using the output of the most up-to-date simulation methodology
instead of the ground-based weather radar and earlier versions of the simulation methodology.
We also present recent progress on the millimeter-wave radiance simulation methodology that is used to derive simulated
global ground-truth data sets for the development of precipitation retrieval algorithms suitable for use on a global scale by
spaceborne millimeter-wave spectrometers. The methodology utilizes the MM5 Cloud Resolving Model (CRM), at 1-km
resolution, to generate atmospheric thermodynamic quantities (for example, humidity and hydrometeor profiles). These data
are then input into a Radiative Transfer Algorithm (RTA) to simulate at-sensor millimeter-wave radiances at a variety of
viewing geometries. The simulated radiances are filtered and resampled to match the sensor resolution and orientation.