With the increasing deployments of CubeSat and SmallSats by both Government and Commercial entities, there is a need for innovative sensors, techniques and applications. These solutions have to be compact, low power, and with improved efficiencies. Rapid progress has been made in innovative methods and sensors for detection of UV/Visible/Infrared radiation for applications in Earth Remote Sensing and other commercial areas.

Since the community has graduated from amateur experiments in the universities to building highly capable CubeSats, it’s time to look into possible science applications of these platforms. There is always a question of calibration traceability of large amount of data acquired from these CubeSat and SmallSat missions. Few of the missions are able to carry calibration hardware on board and produce calibrated data. However, some of these platforms are really compact with no space for any calibration hardware. One of the examples is the use of other large missions as transfer radiometer for earth imaging CubeSat constellations. We also have to look at other options like vicarious methods and other innovative techniques to acquire scientifically meaningful data.

The session is a high-level forum bringing together scientists and technologists involved in the research, design, and development of CubeSats for Earth Remote Sensing applications. This session comprises invited presentations by scientists presenting the data from past and present missions and show science traceability by comparing them with data from large missions. For example data from TEMPEST-D, HARP, TROPICS will be presented with their approach to calibration and validation.

In total there will be total of five presentations, including the overview and four missions presenting their latest data with their calibration approach.

The HyTI (Hyperspectral Thermal Imager) mission, funded by NASA’s Earth Science Technology Office InVEST (In-Space Validation of Earth Science Technologies) program, will demonstrate how high spectral and spatial long-wave infrared image data can be acquired from a 6U CubeSat platform. The mission will use a spatially modulated interferometric imaging technique to produce spectro-radiometrically calibrated image cubes, with 25 channels between 8 to 10.7 microns, at 13 wavenumber resolution), at a ground sample distance of approximately 60 m. The HyTI performance model indicates narrow band NEdTs of less than0 .3 K. The small form factor of HyTI is made possible via the use of a no-moving-parts Fabry-Perot interferometer, and JPL’s cryogenically-cooled (NEdT requirement can be met at dark current associated with an FPA temperature of 68 K) HOT-BIRD FPA technology. Launch is scheduled for summer 2022. The value of HyTI to Earth scientists will be demonstrated via on-board processing of the raw instrument data to generate L1 and L2 products, with a focus on rapid delivery of data regarding volcanic degassing, and land surface temperature.

HyTI uses JPL's T2SLS ‘HOT-BIRD’ focal plane array. T2SLS detectors exhibit high levels of temporal stability with respect to both gain and offset, making them an ideal candidate for HyTI, as the 6U form-factor left no room for an onboard radiometric calibration mechanism. Rather, prior to launch, the HyTI instrument will be calibrated by deriving look-up tables relating target radiance and sensor response for a suite of FPA integration times and temperatures. On-orbit, data will be calibrated to spectral radiance using these gain LUTs. It is anticipated that radiometric offset (obtained via deep space look) will be updated each orbit.

During operations the HyTI calibration will be validated using three sources: i) occasional Lunar imaging events, ii) vicarious calibration with Landsat TIIRS and Terra ASTER data sets, and iii) direct validation using the Jet Propulsion laboratory’s Lake Tahoe and Salton Sea calibration sites. This will be important, as HyTI will process from L0 to L1 on-orbit, and so the calibration must be validated (and if required, updated) in a timely manner (as most L0 data will not be transmitted to ground or archived).

In this presentation we will provide an overview of the HyTI measurement approach, the onboard data reduction and calibration approach and the spacecraft design.

The 3U Hyper-Angular Rainbow Polarimeter (HARP) Cubesat carries a compact hyper-angular imaging polarimeter (size of a small loaf of bread) aimed at the multiwavelength polarized imaging of Earth’s atmosphere from different viewing angle perspectives. The HARP system consists of a wide field of view lens, followed by a polarization optimized Philips prism, and three imaging sensors. Each sensor is furnished with a linear polarizer at a particular orientation, and a stripe filter that simultaneously select the sampled wavelengths, and the along track viewing angle for each pushbroom imager. HARP started data collection in April 2020 from the ISS orbit and is the first Hyper-Angular imaging polarimeter in space. The HARP payload produces pushbroom images at four wavelengths (440, 550, 670 and 870nm) with up to 60 viewing angles at 670 nm and up to 20 along track angles for the other three wavelengths. HARP swath consists of 94 degs in the cross track direction, allowing for a very wide coverage around the globe, and +/-57 degs in the along track direction, providing wide scattering angle sampling for aerosol and cloud particle retrieval. The HARP satellite is still active on orbit and so far have produce a large collection of scenes providing an unprecedented demonstration of the hyperangular retrieval of cloud and aerosol properties from space.

The HARP sensor was radiometrically and polarimetrically calibrated at the ground, and its post launch radiometric calibration have been intercompared with other satellite sensor including MODIS, VIIRS and ABI showing excellent results over its first year of operation. Multiple ground targets have been selected for calibration, including the high altitude lake Titicaca, in the border between Peru and Bolivia, which allow for polarized sunglint measurements with little atmospheric interference. A first cut in HARP’s post-launch polarimetric calibration has also being assessed by comparing the HARP measurements with multi-angle surface and atmospheric models. Results from this intercomparison will be discussed as part of this presentation.

In terms of level 2 performance, the Generalized Retrieval of Aerosol and Surface Properties (GRASP) algorithm has being used for the detailed retrieval of aerosol and surface properties using HARP CubeSat data. GRASP has been applied to multiple HARP scenes producing retrievals of dust, smoke, pollution and other aerosol components, including the measurements of aerosol optical depth, real and complex refractive indices, particle sphericity, single scattering albedo, etc. These retrievals will be presented and discussed in detail showing dust transport from Africa, forest fire smoke, etc. HARP has also performed the first ever hyper-angular retrieval of cloud microphysical properties using cloudbow measurements. Different than previous retrievals, the hyperangular measurements from HARP allow for cloudbow measurements with pixel resolution rather than using a composite of a large area as it has been performed by the POLDER instrument.

This presentation will discuss the performance of the HARP sensor in space tracked by intercomparisons with other satellites and general ground-based data sets. The HARP payload is a precursor to the HARP-2 polarimeter that will fly on the NASA PACE mission to collect global data on aerosol and cloud particles, which will also be introduced as part of this talk.

Temporal Experiment for Storms and Tropical Systems – Demonstration (TEMPEST-D) is a nearly 3-year NASA mission to demonstrate global observations from a multi-frequency microwave sensor deployed on a 6U CubeSat platform. TEMPEST was proposed in 2013 as an Earth Venture Instrument-2 to perform high temporal resolution observations of rapidly evolving storms using a constellation of five identical CubeSats with microwave sensors in a single orbital plane, providing 7-minute temporal sampling of rapidly-developing convective activity over 30 minutes. To demonstrate necessary capability to successfully operate the TEMPEST constellation, NASA’s Earth Venture Technology program funded the production, deployment and operation of a TEMPEST-D, a multi-frequency microwave radiometer on a 6U CubeSat, which was successfully delivered for launch less than 2 years after PDR.

TEMPEST-D was deployed from the ISS into low Earth orbit on July 13, 2018, and observed the Earth’s atmosphere nearly continuously until it re-entered on June 21, 2021. TEMPEST-D performed the first global Earth observations from a multi-frequency microwave radiometer on a CubeSat. The TEMPEST-D mission substantially exceeded expectations in terms of data quality, stability, consistency and mission duration. TEMPEST-D data were validated through inter-calibration with existing scientific and operational microwave sensors measuring at similar frequencies, including 4 MHS sensors on NOAA-19, MetOp-A, -B and -C, as well as GPM/GMI. These validation results showed that TEMPEST had comparable or better performance to much larger operational sensors in terms of instrument noise, calibration accuracy, precision and stability throughout the nearly 3-year mission.

TEMPEST-D performed detailed observations of the microphysics of hurricanes, typhoons and tropical cyclones during three consecutive hurricane seasons. Simultaneous observations by TEMPEST-D and JPL’s RainCube weather radar demonstrated physical consistency and well-correlated passive and active microwave measurements of severe weather from the two CubeSats. Quantitative precipitation estimates retrieved from TEMPEST-D data are highly correlated with standard ground radar precipitation products. TEMPEST-D also performed along-track scanning measurements constituting the first space-borne demonstration of “hyperspectral” microwave sounding observations to retrieve the height of the planetary boundary layer.

The stability, accuracy and reliability of the TEMPEST-D instrument aboard a 6U CubeSat opens a breadth of possibilities for future science missions to substantially improve the temporal resolution of cloud and precipitation observations. Together, the TEMPEST-D and RainCube CubeSat missions demonstrated the necessary technology and scientific potential to deploy coordinated constellations of small satellites with heterogeneous microwave sensors to improve understanding of microphysical processes of both clouds and precipitation.

The NASA Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission will provide 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. TROPICS will provide rapid-refresh microwave measurements (median refresh rate of approximately 50 minutes for the baseline mission) 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. The TROPICS comstellation mission comprises six CubeSats in three low-Earth orbital planes. Each CubeSat will host a high performance 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. TROPICS spatial resolution and measurement sensitivity is comparable with current state-of-the-art observing platforms. Launches for the TROPICS constellation mission are planned in 2022. NASA’s Earth System Science Pathfinder (ESSP) Program Office approved the separate TROPICS Pathfinder mission, which launched on June 30, 2021, in advance of the TROPICS constellation mission as a technology demonstration and risk reduction effort. 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 instrument checkout and calibration/validation plans and progress for the TROPICS Pathfinder mission and will include first light mission results and comparisons with current operational instruments, such as the Advanced Technology Microwave Sounder (ATMS). We will also discuss plans for the constellation mission, including recent activities to improve the data latency for near-real-time forecasting applications.

SigNals Of Opportunity: P-band Investigation (SNOOPI) will be the first on-orbit demonstration of remote sensing using Signals of Opportunity (SoOp) in P-band (240-380 MHz). P-band SoOp has the potential for spaceborne remote sensing of root-zone soil moisture (RZSM) and snow water equivalent (SWE), two variables identified as priorities in NASA’s 2017-2027 Decadal Survey for Earth Science and Applications from Space. P-band is needed to penetrate through dense vegetation to sense RZSM. The longer wavelength of P-band also increases the unwrapping interval for phase observations, which may enable a new measurement of SWE.

SNOOPI is a technology validation mission with three specific goals to test important assumptions about P-band reflectometry form orbit. First, to collect data from orbit and validate the signal scattering model, most importantly the assumption of a coherent signal. Second, to investigate possible effects of RFI on the measurements, given the prevalence of other sources in these frequencies. Third, to demonstrate robustness to uncertainty in the source location and signal strength. The SoOp observable will be used to estimate complex reflection coefficient over varied topographical land surface conditions and will be compared with forward models driven by in-situ data.

In support of the mission, analysis have been performed on key instrument and mission parameters. Evaluation of the orbital coverage of the spacecraft based on launch date are used to create instrument recording schedules. Priorities for these recordings are overpasses of SMAP Calibration/Validation (cal/val) sites, arcs of data over winter snow-covered regions and tracks on the eastern Contiguous United States (CONUS). Results from an SoOp retrieval analytical model are verified using a bit-level signal and instrument simulator. A ground-based station is designed (soon to be deployed) to monitor the noncooperative sources, in order to reduce risk due to uncertainty in knowledge of the broadcast power, spectrum shape, and orbital position of the transmitter source. SNOOPI is scheduled for delivery in August-2022.