Thursday, 31 August 2023: 9:30 AM
Great Lakes A (Hyatt Regency Minneapolis)
Tomorrow.io is deploying the world’s first commercial cloud and precipitation radar satellites in concert with a passive millimeter-wave sounder constellation to transform the global precipitation observing system. The multi-sensor, low Earth orbit constellation builds on the highly successful demonstration through the Global Precipitation Measurement (GPM) mission of the synergy between these passive-active sensors for spaceborne precipitation observation, while greatly expanding the number of radars and radiometers with an initial planned size of approximately 30 satellites in total. The Tomorrow.io constellation will achieve a mean revisit rate of about 1 hour over the majority of the globe, and will provide near-real-time (15 minute max latency) data products including radar cloud and precipitation profiles, sounder precipitation retrievals, temperature and humidity profiles, and selected surface geophysical observations including ocean wind speed estimates. These instrument data products, with an unprecedented combination of global coverage, high measurement quality, and low latency, will in turn be used to drive Tomorrow.io’s proprietary weather products including global precipitation analyses, short-term precipitation nowcasts, and medium-range NWP forecasts.
The radar satellite development program at Tomorrow.io consists of two distinct phases: a prototype, or “Pathfinder”, phase consisting of two identical non-scanning Ka-band radar satellites, Tomorrow-R1 and Tomorrow-R2, launching on separate vehicles in the first half of 2023; and the subsequent “operational” radar satellite constellation comprised of wide-swath, precipitation mapping Ka-band radar satellites with an initial spaceborne deployment planned for 2024. The Pathfinder phase serves as a technology demonstration and risk reduction effort for key radar subsystems and data processing algorithms, as well as for mission operations capability development, data product calibration and validation, and data pipeline integration for real-time forecasting applications. Building on the Pathfinder capabilities, the operational scanning payload is based on a novel, cross-track scanning design that affords performance similar to that of the Ka-band Precipitation Radar (KaPR) instrument aboard the GPM Core Observatory with significantly reduced system size, weight, and power at a small fraction of the cost. High-level measurement requirements for the operational radar system include wide swath width (400 km), high spatial resolution (5 x 5 x 0.25 km), and high precipitation detection sensitivity (< 12 dBZ).
The Pathfinder and operational payloads are based on Tomorrow.io's proprietary ARENA software-defined radar (SDR), which is a fully digital IF transceiver that supports operation over the entire allocated radar transmit band between 35.5 and 36 GHz. The SDR allows for pulse-to-pulse reconfigurability of the transmit waveform and digital receiver processing parameters, offering unique sampling capabilities for cloud and precipitation sensing as well as the ability to operate in a wideband altimetry mode. While being designed for an operational weather forecasting use case, the mission objectives and requirements for both payloads reflect those of a science-quality application. This includes stringent requirements on the absolute calibration accuracy (<1 dB uncertainty), clutter profile characteristics, and measurement sensitivity and resolution. Furthermore, key to affording such a high level of performance in a SmallSat form-factor is the implementation of long pulse duration pulse compression, which was first demonstrated from orbit with the RainCube Ka-band precipitation radar from NASA's Jet Propulsion Laboratory.
The two identical Pathfinder spacecraft utilize the Corvus XL bus from Astro Digital Inc. and feature a state-of-the-art, all-solid-state radar payload with a 1.2 meter solid Cassegrain reflector antenna that results in a fixed pencil beam with 3 dB width of 0.5 degrees. From the planned orbital altitude of around 500 km, this results in a 3 dB ground footprint at nadir of about 4.5 km. With a peak transmit power of roughly 20 W and duty cycle of 30%, the system realizes very high detection sensitivity (< 10 dBZ) by employing both high-time-bandwidth product pulse compression and frequency diversity, which greatly enhance coherent signal integration and speckle (i.e., fading) noise suppression, respectively, relative to a short pulse radar system without frequency modulation. The nominal precipitation sampling approach utilizes a frequency-diverse burst of linear frequency modulated (LFM) pulses, each with a length of 30-60 microseconds, bandwidth of 1.2 MHz, and a variable waveform taper depending on the relevant range sidelobe objectives. Assuming an along-track averaging interval of 2.25 km consistent with Nyquist sampling of the ground footprint, the radar sensitivity is estimated to be 8 dBZ for a maximum allowable reflectivity uncertainty of 2 dB, while for high-SNR precipitation targets the random measurement uncertainty is 0.1 dB. Furthermore, the SDR's wide instantaneous transmit and receive bandwidth and non-dispersive radar front-end allow for the system to be operated in a wide-bandwidth (nominally 400 MHz), nadir-pointing altimetry mode, with expected precision similar to existing spaceborne pencil-beam altimeters like AltiKa.
The main objectives of the Pathfinder mission are to demonstrate performance of key radar subsystems from a low-cost LEO platform, acquire relevant measurements of precipitation and surface scattering for operational algorithm development, and develop and validate effective on-orbit transceiver calibration methods to enable rapid commissioning of the operational scanning payloads. In this talk, we will present the Pathfinder radar architecture, mission concept of operations, pre-launch instrument characterization and calibration, and initial results from on-orbit payload operations. Furthermore, we present a detailed analysis of the clutter profiles resulting from surface scattering, with particular emphasis on the impact of the measured transmitter phase noise on surface clutter. This analysis reveals a clutter profile that is nearly range-weighing-function limited for all incidence angles and implies a maximum clutter free height of 1 km or less for the conservative case of nadir illumination with no attenuation and surface normalized radar cross section of 12 dB.
The radar satellite development program at Tomorrow.io consists of two distinct phases: a prototype, or “Pathfinder”, phase consisting of two identical non-scanning Ka-band radar satellites, Tomorrow-R1 and Tomorrow-R2, launching on separate vehicles in the first half of 2023; and the subsequent “operational” radar satellite constellation comprised of wide-swath, precipitation mapping Ka-band radar satellites with an initial spaceborne deployment planned for 2024. The Pathfinder phase serves as a technology demonstration and risk reduction effort for key radar subsystems and data processing algorithms, as well as for mission operations capability development, data product calibration and validation, and data pipeline integration for real-time forecasting applications. Building on the Pathfinder capabilities, the operational scanning payload is based on a novel, cross-track scanning design that affords performance similar to that of the Ka-band Precipitation Radar (KaPR) instrument aboard the GPM Core Observatory with significantly reduced system size, weight, and power at a small fraction of the cost. High-level measurement requirements for the operational radar system include wide swath width (400 km), high spatial resolution (5 x 5 x 0.25 km), and high precipitation detection sensitivity (< 12 dBZ).
The Pathfinder and operational payloads are based on Tomorrow.io's proprietary ARENA software-defined radar (SDR), which is a fully digital IF transceiver that supports operation over the entire allocated radar transmit band between 35.5 and 36 GHz. The SDR allows for pulse-to-pulse reconfigurability of the transmit waveform and digital receiver processing parameters, offering unique sampling capabilities for cloud and precipitation sensing as well as the ability to operate in a wideband altimetry mode. While being designed for an operational weather forecasting use case, the mission objectives and requirements for both payloads reflect those of a science-quality application. This includes stringent requirements on the absolute calibration accuracy (<1 dB uncertainty), clutter profile characteristics, and measurement sensitivity and resolution. Furthermore, key to affording such a high level of performance in a SmallSat form-factor is the implementation of long pulse duration pulse compression, which was first demonstrated from orbit with the RainCube Ka-band precipitation radar from NASA's Jet Propulsion Laboratory.
The two identical Pathfinder spacecraft utilize the Corvus XL bus from Astro Digital Inc. and feature a state-of-the-art, all-solid-state radar payload with a 1.2 meter solid Cassegrain reflector antenna that results in a fixed pencil beam with 3 dB width of 0.5 degrees. From the planned orbital altitude of around 500 km, this results in a 3 dB ground footprint at nadir of about 4.5 km. With a peak transmit power of roughly 20 W and duty cycle of 30%, the system realizes very high detection sensitivity (< 10 dBZ) by employing both high-time-bandwidth product pulse compression and frequency diversity, which greatly enhance coherent signal integration and speckle (i.e., fading) noise suppression, respectively, relative to a short pulse radar system without frequency modulation. The nominal precipitation sampling approach utilizes a frequency-diverse burst of linear frequency modulated (LFM) pulses, each with a length of 30-60 microseconds, bandwidth of 1.2 MHz, and a variable waveform taper depending on the relevant range sidelobe objectives. Assuming an along-track averaging interval of 2.25 km consistent with Nyquist sampling of the ground footprint, the radar sensitivity is estimated to be 8 dBZ for a maximum allowable reflectivity uncertainty of 2 dB, while for high-SNR precipitation targets the random measurement uncertainty is 0.1 dB. Furthermore, the SDR's wide instantaneous transmit and receive bandwidth and non-dispersive radar front-end allow for the system to be operated in a wide-bandwidth (nominally 400 MHz), nadir-pointing altimetry mode, with expected precision similar to existing spaceborne pencil-beam altimeters like AltiKa.
The main objectives of the Pathfinder mission are to demonstrate performance of key radar subsystems from a low-cost LEO platform, acquire relevant measurements of precipitation and surface scattering for operational algorithm development, and develop and validate effective on-orbit transceiver calibration methods to enable rapid commissioning of the operational scanning payloads. In this talk, we will present the Pathfinder radar architecture, mission concept of operations, pre-launch instrument characterization and calibration, and initial results from on-orbit payload operations. Furthermore, we present a detailed analysis of the clutter profiles resulting from surface scattering, with particular emphasis on the impact of the measured transmitter phase noise on surface clutter. This analysis reveals a clutter profile that is nearly range-weighing-function limited for all incidence angles and implies a maximum clutter free height of 1 km or less for the conservative case of nadir illumination with no attenuation and surface normalized radar cross section of 12 dB.
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