New satellite constellations to provide high-resolution atmospheric observations from microwave (MW) sounders operating in low-Earth orbit are now coming online and are providing operationally useful data. The first of these missions, the NASA Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) Earth Venture (EVI-3) mission, was successfully launched into orbit on May 7 and 25, 2023 (Eastern Daylight Time, two CubeSats in each of the two launches). TROPICS is now providing nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at high temporal resolution to conduct high-value science investigations of tropical cyclones (TCs). TROPICS is providing rapid-refresh MW measurements (median refresh rate of better than 60 min early in the mission with four functional CubeSats, and now approximately 70–90 min with three functional CubeSats) over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. Hundreds of high-resolution images of TCs have been captured thus far by the TROPICS mission, revealing the detailed structure of the eyewall and surrounding rain bands. The new 205-GHz channel in particular (together with a traditional channel near 92 GHz) is providing new information on the inner storm structure, and, coupled with the relatively frequent revisit and low downlink latency, is already informing TC analysis at operational centers. Here, we present an overview of the TROPICS mission after two years of successful science operations with a focus on the suite of geophysical (Level 2) products (atmospheric vertical temperature and moisture profiles, instantaneous surface rain rate, and TC intensity) and the science investigations that have been enabled by these new measurements.

The four NASA TROPICS Earth Venture (EVI-3) CubeSat constellation satellites were successfully launched into orbit on May 8 and May 26, 2023 (NZST) – two satellites were deployed in each launch. TROPICS is now providing nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at a median refresh rate of approximately 60 minutes to conduct high-value science investigations of tropical cyclones. TROPICS provides microwave measurements in twelve channels spanning 90-205 GHz over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. Hundreds of high-resolution images of tropical cyclones have been captured thus far by the TROPICS mission, revealing detailed structure of the eyewall and surrounding rain bands. The new 205-GHz channel in particular (together with a traditional channel near 91.65 GHz) is providing new information on the inner storm structure, and, coupled with the relatively frequent revisit and low downlink latency, is informing tropical cyclone analysis at operational centers. In this paper, the radiance and geophysical performance of Pathfinder and the constellation satellites is presented, showing that the mission is on track to meet its baseline requirements.

We have developed and implemented a near-real-time retrieval algorithm to estimate temperature and water vapor vertical profiles from TROPICS [1] L1b brightness temperature observations. A neural network approach, with heritage in our past work [2] in the operational Atmospheric Infrared Sounder science products [3], was selected due to fast execution time, overall accuracy, and robustness to a wide variety of meteorological conditions. Here, we describe our methodology, present initial performance results on the TROPICS Pathfinder mission on test data sets, and describe our ongoing efforts to validate the algorithm.

The Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission was selected by NASA as part of the Earth Venture-Instrument (EVI-3) program. TROPICS comprises a constellation of six CubeSats in three low-Earth low-inclination orbital planes. Each CubeSat will host a high performance millimeterwave radiometer to provide temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles. Spatial resolution at nadir ranges from approximately 15 km for the G-band channels to 30 km for the W-band channels. The Pathfinder (Qualification Unit) was launched on June 30, 2021, and the six constellation flight units are scheduled to launch in the first half of 2022. The TROPICS Pathfinder mission has provided an opportunity to checkout and optimize all mission elements prior to the primary constellation mission. This presentation will describe the on-orbit results for the successful TROPICS Pathfinder precursor mission and will highlight numerous technical innovations that have made the TROPICS mission possible and enabled new capabilities for future Earth observing missions [4].

CubeSats with miniaturized microwave radiometers are now demonstrating the potential to provide science-quality weather measurements. For example, the Micro-Sized Microwave Atmospheric Satellite-2A (MicroMAS-2A) and Temporal Experiment for Storms and Tropical Systems–Demonstration (TEMPEST-D) CubeSats are both launched in 2018 and have demonstrated microwave atmospheric sounder data from orbit. The NASA Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission is a follow-on constellation of six 3U CubeSats based on the MicroMAS-2 design that is scheduled for launch no sooner than 2021. The TROPICS sensors use internal noise diodes (NDs) for calibration. Although the NDs on TROPICS are similar to technology flown on GMI, they have not been tested on-orbit at TROPICS frequencies. In order to track and correct ND drift, we develop a novel method of calibration for CubeSat constellations, such as TROPICS, by incorporating periodic solar and lunar intrusions as an additional source of information to counter ND drift. These lunar intrusions also occur for existing satellites hosting microwave radiometers in sun-synchronous polar orbits but are much more infrequent than for the TROPICS constellation’s scanning payload. In this work, we develop a solar/lunar calibration correction algorithm and test it using advanced technology microwave sounder (ATMS) lunar intrusion data. The mean bias and standard deviation between the solar/lunar calibration correction algorithm and actual ATMS data fall within the expected ATMS error budget of 0.6–3.9 K, validating our model.

Passive microwave sounders provide the highest-impact observations ingested by major numerical weather prediction (NWP) forecast models. The Advanced Technology Microwave Sounder (ATMS), built by Northrop Grumman, Azusa, CA, USA, is the latest operational microwave sounder series being launched by the United States to provide both temperature and water vapor soundings of the atmosphere. The first ATMS was launched on the Suomi National Polar-orbiting Partnership (SNPP) satellite in 2011. This article focuses on the details of the on-orbit performance characterization of the second ATMS, which launched on November 18, 2017, on the Joint Polar Satellite System-1 (JPSS-1) satellite. After successful commissioning, JPSS-1 was renamed National Oceanic and Atmospheric Administration (NOAA)-20 (N-20). We present performance characterizations from prelaunch and postlaunch tests, including the thermal vacuum (TVAC) campaign, and postlaunch activities that contribute to the radiance data products. Significant improvements were found for reflector emissivity,$1/f$noise performance, antenna beam efficiency, interchannel noise correlation, and scan drive bearing design. New geolocation and pointing algorithms were evaluated. The N-20 ATMS has the same channel set, polarizations, scan geometry, and calibration approach as the SNPP ATMS. The N-20 ATMS meets all performance requirements with margin.

The Advanced Technology Microwave Sounder (ATMS) is a passive microwave radiometer for the current generation of polar-orbiting meteorological satellites operated by the National Oceanic and Atmospheric Administration (NOAA). The first two ATMS instruments are manifested onboard the Suomi National Polar-orbiting Partnership (S-NPP) and NOAA-20 satellites. Several critical changes have been made to ATMS operational calibration algorithm since March 2017. The calibration processing has been revised from a Rayleigh–Jeans approximated algorithm to a full radiance algorithm in order to reduce the error introduced by the approximation over cold radiances in the higher frequency channels. In addition, based on the lessons learned from S-NPP and NOAA-20 postlaunch calibration/validation tests, some major improvements have been made in the updated operational algorithm. These include reflector emission and antenna pattern corrections. Details of the radiance-based ATMS on-orbit calibration are documented in this report, and results of prelaunch calibration error budget analysis and postlaunch calibration accuracy evaluation are also presented for reference.

This paper describes the TROPICS L1 calibration algorithm. The NASA TROPICS mission [1] hosts a passive microwave radiometer [2] that provides temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles. Noise Diodes (ND) are an attractive option for calibration of small satellite sounders, which replaces the bulky and heavy internal iron-filled epoxy calibration target that is difficult to shield from the sun [3]. The TROPICS radiome-ter's pre-launch thermal-vacuum testing characterized the ND output temperature and the radiometer's non-linearity, and also verified the characterization using parts of the algorithm described in this paper[4].

Reported here are disk-integrated Moon surface microwave brightness temperature ($Tb$) retrievals covering the frequency range of 23–183 GHz. Full Moon observations obtained from the advanced technology microwave sounder (ATMS) onboard the NOAA-20 satellite during a special spacecraft pitch–maneuver operation forms the basis of the retrievals. Instrument nonlinearity, Earth sidelobe contamination, cosmic background radiation, and reflector thermal emission corrections are applied to the observations to obtain accurate values of the Moon’s$Tb$at all frequencies. The measured full Moon$Tb$ranges from ~240 to 293 K with frequency increases from 23 to 183 GHz. A clear frequency trend is detected when the brightness temperature increases.

The Microsized Microwave Atmospheric Satellite (MicroMAS-2A) is a 3U CubeSat that was launched in January 2018 as a technology demonstration for future microwave sounding constellation missions, such as the NASA Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission now in development. MicroMAS-2A has a miniaturized 1U ten-channel passive microwave radiometer with channels near 90, 118, 183, and 206 GHz for moisture and temperature profiling and precipitation imaging [4]. MicroMAS-2A provided the first CubeSat atmospheric vertical sounding data from orbit, and to date it is the only CubeSat to provide temperature and moisture sounding and surface imaging. In this article, we analyze six segments of data collected from MicroMAS-2A in April 2018 and compare them to ERA5 reanalysis fields coupled with the Community Radiative Transfer Model (CRTM). This initial assessment of CubeSat radiometric accuracy shows biases relative to ERA5 with magnitudes ranging from 0.4 to 2.2 K (with standard deviations ranging from 0.7 to 1.2 K) for the four mid-tropospheric temperature channels and biases of 2.2 and 2.8 K (standard deviations 1.8 and 2.6 K) for the two lower tropospheric water vapor channels.

A NOAA-20 (N20) Advanced Technology Microwave Sounder (ATMS) active geolocation (GEO) test was performed around January 2018 with 24 preselected coastline crossing scenes. After a comprehensive analysis of ATMS stare data and the corresponding Visible Infrared Imaging Radiometer Suite (VIIRS) data, the ATMS pitch, roll, and yaw pointing angle errors are found from the nadir perpendicular, the nadir oblique shallow angle, and the off-nadir perpendicular coastline crossing data, respectively. In this study, we first determine the ATMS radiometric coastline crossing time by using the ATMS radiometric count data. Since the coastline can be located anywhere within one ATMS field of view (FOV) from the passive (regular scanning) GEO data, depending on the scan starting time, it is not a valid assumption for the inflection point being the same as the coastline location. Consequently, using the passive GEO data to validate the sensor’s on-orbit pointing angle performance is limited. After finding the ATMS radiometric coastline crossing time from the ATMS data, we compare it with the VIIRS effective time stamp. Specifically, the VIIRS M3, M4, and M5 (true color) and M15 and M16 bands (thermal) data have a much smaller footprint size. Using the differences of the ATMS and VIIRS (effective) coastlines crossing times, the N20 ATMS pitch, roll, and yaw pointing angle errors are found to be −0.09°, −0.24°, and 0.28°, respectively. To determine ATMS GEO properly, these on-orbit pointing errors need to be corrected, adding to the ATMS sensor data record (SDR) processing coefficient table, and passed on to the operational GEO processing code.

The Advanced Technology Microwave Sounder (ATMS) is a satellite-based microwave radiometer that provides temperature and humidity sounding observations from low Earth orbit. The instrument utilizes 22 channels that cover a frequency range of 23 to 183 GHz. The first ATMS instrument was launched in 2011 on the Suomi National Polar-orbiting Partnership (S-NPP) satellite and the second ATMS was launched in 2017 on the Joint Polar Satellite System-1 (JPSS-1) satellite (now NOAA-20); both on-orbit ATMS instruments are currently operational. This paper will describe the pre-launch performance of the third ATMS instrument, designated for the JPSS-2 satellite, during ground testing and calibration.

The NASA TROPICS mission [1] hosts a high performance radiometer to estimate temperature and water vapor profiles, precipitation, and Tropical Cyclone intensity. Noise Diodes (ND) are an attractive option for calibration of small satellite sounders, especially in the face of volume constraints that preclude extensive radiative shielding of internal calibration targets that is utilized in operational missions [2]. Recent operational missions [3], [4] demonstrated on-orbit ND calibration stability better than 0.1 K over more than four years when prelaunch screening of the ND is used. An essential step for TROPICS is the precise prelaunch characterization of the ND performance over a variety of thermal conditions, which will be augmented by post-launch cross-comparisons similar to the techniques used by the GPM Intercalibration (X-CAL) Working Group. This paper introduces the first radiometric calibration and verification with the radiometer integrated on the satellite platform under flight-like conditions.

For the on-orbit calibration of passive microwave radiometers, instrument non-linearity is a major error source, causing a scene-temperature-dependent error if not being properly corrected. non-linearity results from the intrinsic feature of the square-law detector and amplifiers used in total-power microwave radiometers, and can only be accurately characterized through the ground-based Thermal Vacuum Test (TVAC). The ground-based non-linearity characterization is then used in the calibration algorithm to attempt to remove this error source. Evaluation results for current operational microwave-sounding instruments show that the magnitude of the non-linearity error varies from channel to channel and from instrument to instrument, with maximum changes of several tenths of kelvins to several kelvins. While the different responses of the detector and amplifier may explain the non-linearity differences in different instruments, errors in TVAC tests could also increase the uncertainty in the non-linearity assessment. Therefore, accurate knowledge of error sources in the TVAC test and their corrections are important for a reliable and accurate non-linearity measurement. In this paper, major error sources in the TVAC test are studied and identified for the NOAA-20 Advanced Technology Microwave Sounder. Correction methods are developed by combining the pre-launch TVAC test and post-launch deep-space-scan test data sets. An on-orbit evaluation method is also proposed to validate the ground-measured instrument non-linearity.

This paper evaluates the performance of the passive microwave spectrometer to be launched aboard the Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) for retrieving surface precipitation and hydrometeor water paths. The retrieval algorithms employ neural networks trained and evaluated using the physical reference model NCEP/WRF/TBSCAT/F( λ). Results show that TROPICS retrieved surface precipitation rates and hydrometeor water paths agree well with WRF truth. The accuracies of TROPICS retrieved daily, weekly, and monthly surface precipitation amounts are close to those of the Advanced Microwave Sounding Unit (AMSU). The TROPICS constellation will provide useful precipitation retrievals at unprecedented 30-minute temporal resolution.

The Advanced Technology Microwave Sounder (ATMS) is a space-based, cross-track radiometer for operational atmospheric temperature and humidity sounding, utilizing 22 channels over a frequency range from 23 to 183 GHz. The ATMS for the Joint Polar Satellite System-1 has undergone two rounds of rework in 2014-2015 and 2016, following performance issues discovered during and following thermal vacuum chamber (TVAC) testing at the instrument and observatory level. Final shelf-level testing, including measurement of pass band characteristics and spectral response functions, was completed in December 2016. Final instrument-level TVAC testing and calibration occurred during February 2017. Here we will describe the instrument-level TVAC calibration process, and illustrate with results from the final TVAC calibration effort.

We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earth's limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50-60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015.

The Micro-sized Microwave Atmospheric Satellite (MicroMAS) is a 3U CubeSat (10×10×34 cm, ~4 kg) hosting a passive microwave spectrometer operating near the 118.75-GHz oxygen absorption line. MicroMAS is a dual-spinning 3U CubeSat that aims to address the need for low-cost, mission-flexible, and rapidly deployable spaceborne sensors. The focus of the current MicroMAS mission is to observe convective thunderstorms, tropical cyclones, and hurricanes from a near-equatorial orbit.

We introduce a new technique for absolute “through-theantenna” calibration of cross-track-scanning passive microwave radiometers viewing earth from a low-earth orbit. This method offers significant advantages, in that neither internal calibration targets nor noise diodes are needed to calibrate the radiometer. The algorithm does require periodic updates of the atmospheric state, which can be readily provided by GPS radio occultation observations, for example. An iterative algorithm retrieves the radiometer gain given a sequence of observations of the earth's limb. The algorithm uses a parameterized radiative transfer model of a spherically-stratified atmosphere. The algorithm works best for opaque temperature sounding channels. This method, when used on idealized radiometer measurements (impulse response functions in frequency and space), yields calibration accuracies similar to those that could be obtained with ideal internal calibration targets. This analysis is based on global Monte Carlo simulations using the NOAA88b profile set. An analysis will also be presented showing how calibration performance degrades as the radiometer characteristics deviate from the ideal case. Among the factors considered are: 1) antenna pattern, 2) spectral passband, 3) pointing errors, 4) atmospheric state variability, 5) the number of limb observations required, and 6) sensitivity to sensor noise.

The Suomi NPP spacecraft pitchover maneuver revealed an ATMS scan angle-dependent bias when viewing deep space, which is a homogenous and unpolarized source that fills the entire ATMS Field of Regard. Reflector emissivity was investigated as a possible root cause. The emissivity is polarization dependent, which results in a scan-dependent bias with the quasi-vertical channels having a different bias shape than the quasi-horizontal channels. The normal emissivity was empirically estimated by minimizing the scan bias during the pitchover maneuver, and the reflector's temperature was derived from ATMS telemetry. The model, calibration change, and estimated normal emissivity were verified using the ATMS thermal vacuum test data. Reflector emissitivies from approximately 0.2% to 0.4% were derived, resulting in brightness temperature corrections of up to 0.5 K.

The Micro-sized Microwave Atmospheric Satellite (MicroMAS) is a 3U cubesat (34×10×10 cm, 4.5 kg) hosting a passive microwave spectrometer operating near the 118.75-GHz oxygen absorption line. The focus of the first MicroMAS mission (hereafter, MicroMAS-1) is to observe convective thunderstorms, tropical cyclones, and hurricanes from a near-equatorial orbit at approximately 500-km altitude. A MicroMAS flight unit is currently being developed in anticipation of a 2014 launch. A parabolic reflector is mechanically rotated as the spacecraft orbits the earth, thus directing a cross-track scanned beam with FWHM beamwidth of 2.4-degrees, yielding an approximately 20-km diameter footprint at nadir incidence from a nominal altitude of 500 km. Radiometric calibration is carried out using observations of cold space, the earth's limb, and an internal noise diode that is weakly coupled through the RF front-end electronics. A key technology feature is the development of an ultra-compact intermediate frequency processor module for channelization, detection, and A-to-D conversion. The antenna system and RF front-end electronics are highly integrated and miniaturized. A MicroMAS-2 mission is currently being planned using a multi-band spectrometer operating near 118 and 183 GHz in a sun-synchronous orbit of approximately 800-km altitude. A HyMAS-1 (Hyperspectral Microwave Atmospheric Satellite) mission with approximately 50 channels near 118 and 183 GHz is also being planned. In this paper, the mission concept of operations will be discussed, the radiometer payload will be described, and the spacecraft subsystems (avionics, power, communications, attitude determination and control, and mechanical structures) will be summarized.

Recent technology advances have profoundly changed the landscape of modern radiometry by enabling miniaturized, low-power, and low-noise radio-frequency receivers operating at frequencies near 200 GHz and beyond. These advances enable the practical use of receiver arrays to multiplex multiple broad frequency bands into many spectral channels. We use the term “hyperspectral microwave” to refer generically to microwave sounding systems with approximately 50 spectral channels or more. In this paper, we report on the design and analysis of the receiver subsystem (lensed antenna, RF front-end electronics, and IF processor module) for the Hyperspectral Microwave Atmospheric Sounder (HyMAS) comprising multiple receivers near the oxygen absorption line at 118.75 GHz and the water vapor absorption line at 183.31 GHz. The hyperspectral microwave receiver system will be integrated into a new scanhead compatible with the NASA GSFC Conical Scanning Microwave Imaging Radiometer/Compact Submillimeter-wave Imaging Radiometer (CoSMIR/CoSSIR) airborne instrument system to facilitate demonstration and performance characterization under funding from the NASA ESTO Advanced Component Technology program. Four identical radiometers will be used to cover 108-119 GHz, and two identical receivers will be used to cover 173-183 GHz. Subharmonic mixers will be driven by frequency-multiplied dielectric resonant oscillators, and single-sideband operation will be achieved by waveguide filtering of the lower sideband. A relatively high IF frequency is chosen to facilitate miniaturization of the IF processor module, which will be fabricated using Low Temperature Co-fired Ceramic (LTCC) technology. Corrugated feed antennas with lenses are used to achieve a FWHM beamwidth of approximately 3.5 degrees. Two polarizations are measured by each feed to increase overall channel count, and multiple options will be considered during the design phase for the polarization diplexing approach. Broadband operation over a relatively high intermediate frequency range (18-29 GHz) is a technical challenge of the front-end receiver systems, and a receiver temperature of approximately 2000-3000K is expected over the receiver bandwidth. This performance, together with approximately 100-msec integration times typical of airborne operation, yields channel NEDTs of approximately 0.35K, which is adequate to demonstrate the hyperspectral microwave concept by comparing profile retrievals with high-fidelity ground truth available either by coincident overpasses of hyperspectral infrared sounders and/or in situ radiosonde/dropsonde measurements.

This paper develops a precipitation retrieval algorithm for the Advanced Technology Microwave Sounder (ATMS) recently launched aboard the U.S. Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. The algorithm is called the ATMS MIT Precipitation retrieval algorithm version 1 (ATMP-1), employs neural network estimators trained and evaluated using the validated global reference physical model NCEP/MM5/TBSCAT/F(λ), and works for snow-free land and seawater with |latitudes|<;50°. Signals were carefully chosen and principal component analysis was used to filter out angle and surface effects, and other noises. Retrievals are useful for surface precipitation rates higher than 1 mm/h at 15-km resolution for both land and sea, as evaluated using MM5. Surface precipitation rates retrieved using ATMP-1 for ATMS aboard Suomi NPP satellite are in good agreement with those retrieved using the AMSU MIT Precipitation retrieval algorithm (AMP) for AMSU aboard NOAA-18 satellite.

A suite of sensors scheduled to fly onboard the NPOESS Preparatory Project (NPP) satellite in 2011 will continue the Sensor Data Records (SDRs) provided by operational and research missions over the last 40 years. The Cross-track Infrared and Microwave Sounding Suite (CrIMSS), consisting of the Cross-track Infrared Sounder (CrIS) and the first space-based, Nyquist-sampled cross-track microwave sounder, the Advanced Technology Microwave Sounder (ATMS), will provide atmospheric vertical profile information to improve numerical weather and climate modeling. The ability of ATMS to sense temperature and moisture profile information in the presence of non-precipitating clouds complements the high vertical resolution of CrIS. Furthermore, the ability of ATMS to sense scattering of cold cosmic background radiance from the tops of precipitating clouds allows the retrieval of precipitation intensities with useful accuracies over most surface conditions. This paper will present several assessments of the performance of ATMS. Prelaunch testing of ATMS has characterized the principal calibration parameters and has enabled predictions of on-orbit performance with high levels of confidence. Also to be discussed is the planned on-orbit characterization of ATMS, which will further improve both the measurement quality and the understanding of various error contributions.

Radiometric digital count data are required to test the operational software of the Advanced Technology Microwave Sounder (ATMS) prior to its launch in 2011 to verify effective calibration procedures and optimize performance. These data, however, do not exist prior to launch, thus necessitating a method to build a model of the ATMS that synthesizes realistic data as though the sensor were space-borne. A method to build such a model is described in this paper. The procedure and application are specific to the ATMS but could be applied to other passive microwave radiometers as well.

We introduce a new hyperspectral microwave remote sensing modality for atmospheric sounding, driven by recent advances in microwave device technology that now permit receiver arrays that can multiplex multiple broad frequency bands into more than 100 spectral channels, thus improving both the vertical and horizontal resolutions of the retrieved atmospheric profile. Global simulation studies over ocean and land in clear and cloudy atmospheres using three different atmospheric profile databases are presented that assess the temperature, moisture, and precipitation sounding capability of several notional hyperspectral systems with channels sampled near the 50-60-, 118.75-, and 183.31-GHz absorption lines. These analyses demonstrate that hyperspectral microwave operation using frequency multiplexing techniques substantially improves temperature and moisture profiling accuracy, particularly in atmospheres that challenge conventional nonhyperspectral microwave sounding systems because of high water vapor and cloud liquid water content. Retrieval performance studies are also included that compare hyperspectral microwave sounding performance to conventional microwave and hyperspectral infrared approaches, both in a geostationary and a low-Earth-orbit context, and a path forward to a new generation of high-performance all-weather sounding is discussed.

We introduce a new hyperspectral microwave remote sensing modality for atmospheric sounding, driven by recent advances in microwave device technology that now permit receiver arrays that can multiplex multiple broad frequency bands into more than ~ 100 spectral channels, thus improving both the vertical and horizontal resolution of the retrieved atmospheric profile. Global simulation studies over ocean and land in clear and cloudy atmospheres using three different atmospheric profile databases are presented that assess the temperature, moisture, and precipitation sounding capability of several notional hyperspectral systems with channels sampled near the 50-60-GHz, 118.75-GHz, and 183.31-GHz absorption lines. These analyses demonstrate that hyperspectral microwave operation using frequency multiplexing techniques substantially improves temperature and moisture profiling accuracy, especially in atmospheres that challenge conventional non-hyperspectral microwave sounding systems because of high water vapor and cloud liquid water content. Retrieval performance studies are also included that compare hyperspectral microwave sounding performance to conventional microwave and hyperspectral infrared approaches, both in a geostationary and low-earth orbit context, and a path forward to a new generation of high-performance all-weather sounding is discussed.

As a part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) and the NPOESS Preparatory Project (NPP), 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 [1]. In preparation for the NPOESS/NPP launch, porting and testing of the CrIMSS Environmental Data Record (EDR) algorithms need to be performed.

Spatially oversampled radiometric measurements of the Earth's surface and atmosphere can be reprocessed to optimize various performance metrics. These metrics include resolution, signal-to-noise ratio, and accuracy of retrieved environmental data. In this study, we explore several strategies for two-dimensional image processing for microwave sounder observations and assess the performance using several metrics. Simulated measurements of the Advanced Technology Microwave Sounder (ATMS), the Microwave Imager/Sounder (MIS), and the Geostationary Microwave Array Spectrometer (GeoMAS) are used in the evaluation. We examine spatial filtering (a modification of the effective spatial resolution of the measurements), and in the ATMS case, resampling (a modification of the effective boresight of the composite footprint).

This paper outlines the results of two recent efforts to use the NPOESS Aircraft Sounder Testbed-Microwave (NAST-M) airborne sensor to directly validate the microwave radiometers on a number of operational satellites. 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 1 K for most channels. Comparison results for ocean underflights of the Aqua, NOAA, and MetOp-A satellites are shown.

This manuscript focuses on recent efforts for the development and validation of passive microwave precipitation retrieval algorithms for the NPOESS (National Polar-orbiting Operational Environmental Satellite System) satellite program. Emphasis will be placed on the following three critical components: a methodology for simulating passive microwave observations, a technique for validating the methodology with aircraft measurements, and a statistics-based algorithm for estimating precipitation rate.

This paper will present efforts for the development and validation of passive microwave precipitation retrieval algorithms for the NPOESS (national polar-orbiting operational environmental satellite system) satellite program and the NPOESS preparatory project (NPP) prior to the launch of the first satellite in 2009. The advanced technology microwave sounder (ATMS) offers improvements including finer sampling and spatial resolution over heritage instruments such as the advanced microwave sounding unit instruments AMSU-A/B aboard the NOAA-15, NOAA-16, and NOAA-17, and similar instruments. The conical scanning microwave sounder (CSMS) is planned for the second and subsequent NPOESS satellites. A system for simulating ATMS and CSMS microwave observations from atmospheric data has been developed. This system has shown encouraging results when validated with observations from AMSU-B on NOAA-16. This system is flexible and can be used not only with cross-track scanning instruments but also with conically scanning instruments. A neural network was trained to estimate 5.2deg MM5 rain rates from simulated ATMS observations. Encouraging agreement was observed. However, this algorithm is only preliminary and many improvements are in progress.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed-Microwave (NAST-M) includes spectrometers operating near the oxygen lines at 50-57, 118.75, and 424.76 GHz, and a spectrometer centered on the water vapor absorption line at 183.31 GHz. All four of the spectrometers' antenna horns are collocated, have 3-dB (full-width at half-maximum) beamwidths of 7.5/spl deg/, and are directed at a single mirror that scans cross-track beneath the aircraft with a swath up to 100-km wide. The first part of the paper describes the instrumentation and calibration for the newly installed spectrometers at 183.31 and 424.76 GHz. The second part demonstrates the potential performance of NAST-M, by presenting radiance images and precipitation rate and cell-top retrievals obtained during overflights of isolated convective storm cells, and by comparing these results with coincident visible images. NAST-M radiances are also compared with visible, infrared, and radar images. The nonlinear retrieval method was trained with a simple precipitation model. The data were obtained during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE 2002) and the Pacific THORpex (THe Observing-system Research and predictability experiment) Observing System Test (PTOST 2003).

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed-Microwave, or NAST-M , has added two spectrometers to its original suite of spectrometers operating near the oxygen lines at 50-57 GHz and the oxygen line at 118.75 GHz. The NAST-M suite now includes a spectrometer that is centered on the water vapor absorption line at 183.31 GHz, and another that is centered on the oxygen absorption line at 424.76 GHz. This addition has increases the ability of NAST-M to retrieve humidity profiles and to sense smaller-diameter hydrometeors. All four of the spectrometers' horns are collocated, have 3-dB (full-width at half-max) points of 7.5/spl deg/, and are directed at a single scanning mirror, which produces a cross-track scan beneath the aircraft with a swath width of approximately 100 km. Aircraft carrying NAST-M cruise at altitudes of 17 to 20 km, yielding a nadir surface spatial resolution of /spl sim/ 2.6 km.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed-Microwave, or NAST-M, has added two spectrometers to its original suite operating near the oxygen lines at 50-57 GHz and the oxygen line at 118.75 GHz. These new spectrometers are centered on the water vapor absorption line at 183.31 GHz and the oxygen absorption line at 424.76 GHz. This addition has increased the ability of NAST-M to retrieve humidity profiles and to sense smaller-diameter hydrometeors. The co-aligned NAST-M suite concurrently imaged clouds and convective cells during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE 2002) and the 2003 Pacific THORpex (The Observing-system Research and predictability experiment) Observing System Test (THORpex 2003).

The National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed (NAST) has been developed and deployed on the NASA ER-2 high-altitude aircraft. The testbed consists of two co-located cross-track scanning instruments: a Fourier transform interferometer spectrometer (NAST-I) with spectral coverage of 3.7-15.5 /spl mu/m and a passive microwave spectrometer (NAST-M) with 17 channels near the oxygen absorption lines at 50-57 GHz and 118.75 GHz. The testbed provides the first coregistered imagery from high-resolution microwave and infrared sounders and will provide new data that will help (1) validate meteorological satellite environmental data record feasibility, (2) define future satellite instrument specifications, and (3) demonstrate operational issues in ground validation, data calibration, and retrievals of meteorological parameters. To help validate the performance and potential of NAST-M, imagery was collected from more than 20 overpasses of hurricanes Bonnie and Earl during the Convection and Moisture Experiment (CAMEX-3), Florida, boreal summer 1998. The warm core and convection morphology of Hurricane Bonnie (August, 1998) is clearly revealed both by aircraft-based microwave brightness temperature imagery and temperature retrievals within the eye. Radiance comparisons with the Advanced Microwave Sounding Unit on the NOAA-15 satellite and radiosonde observations yield root mean-squared agreements of approximately 1 K or less.