In this study, we present an unsupervised methodology for detecting moving targets using Capella Space’s latest generation SAR sensor. The sensor has the capability to dwell on a target for an extended period of time in its spot-light (SP) mode, which we take advantage of to track moving objects in an acquisition. An approach that combines a signal-processing-based workflow with an image-domain-based one is presented. From one side, the long-dwell SAR image is exploit by doing an interfeometric processing of different azimuth sub-apertures from the long-dwell. From another side, a kernelized cross correlation technique is used. By combining intermediate results from these complementary workflows, a smooth and robust track is obtained on the targets. The algorithm is demonstrated on a long-dwell spotlight obtained over a busy shipping channel with watercraft both small and large successfully tracked.

The ability to automatically detect hard targets is highly beneficial for an imagery analyst. Their initial task in the information gathering process is to identify and interpret these targets in a scene. By automating the detection process, the workflow can be expedited. This paper presents an algorithm for detecting hard targets in long dwell spotlight (SP) Capella Space SAR images. The spectrum of the SP image is divided into non-overlaping sub-bands in order to compute the interferometric coherence between them. The proposed algorithm is tested on real spaceborne Capella SAR data showing the potential to clearly identify hard targets such as buildings, vehicles, and other artificial man-made objects.

Capella Space is the first US commercial company to build, launch, and operate a constellation of synthetic aperture radar satellites capable of collecting very high resolution SAR imagery. All satellites in the constellation carry an X-band radar capable of acquiring imagery in spotlight, sliding spotlight, and stripmap modes. In 2023, Capella will launch the first of a new generation of satellites names Acadia. These satellites will provide high quality imagery and lay the platform for advanced SAR data products, such as interferometric SAR and bistatic imagery.

Temporal Experiment for Storms and Tropical Systems-Demonstration (TEMPEST-D) is a 6U CubeSat satellite with a cross-track scanning millimeter-wave radiometer measuring at five frequencies from 87 to 181 GHz. It employs a direct-detection architecture with InP HEMT monolithic microwave integrated circuit (MMIC) low-noise amplifiers and related new technologies. An end-to-end two-point external calibration is performed every 2-s rotation of the scanning mirror, based on observations of the cosmic microwave background and an internal blackbody calibration target, with three thermistors to monitor the target physical temperature. Corrections for antenna pattern effects and cross-scan biases based on prelaunch measured values were updated using data from an on-orbit calibration pitch maneuver. Validation of the observed brightness temperatures ( TB) is performed by comparing to coincident nonprecipitating ocean observations from five well-calibrated on-orbit instruments, including Global Precipitation Measurement (GPM) mission Microwave Imager (GMI) and four Microwave Humidity Sounder (MHS) sensors on board NOAA-19, MetOp-A, MetOp-B, and MetOp-C satellites. Absolute calibration accuracy is within 1 K for all channels, well within the 4-K requirement. Calibration precision, or stability over time, is within 0.6 K for all channels, also well within the 2-K requirement. The intrinsic noise of TEMPEST-D is lower than MHS, resulting in similar on-orbit noise equivalent differential temperatures (NEDTs), even though TEMPEST-D has a much shorter integration time of 5 ms as compared to 18 ms for MHS. As a result, although the TEMPEST-D radiometer is substantially smaller, lower power, and lower cost than similar current operational radiometers, it has comparable or better performance in terms of instrument noise, calibration accuracy, and calibration stability or precision.

TEMPEST-D is a 6U CubeSat with a payload of a 5-channel millimeter wave cross-track scanning radiometer. It is a technology demonstration mission with requirements of 2 K precision and 4 K absolute calibration. Since its deployment from the International Space Station in July of 2018, the TEMPEST-D team has focused efforts on validating the calibration of the instrument by comparing with similar well-calibrated operational sensors. Such comparisons have shown the instrument to be very well calibrated and stable, with very low noise, well within the requirements. Efforts have subsequently focused on demonstrating that the data can be used for various science applications, including water vapor and cloud water/ice retrievals and data assimilation.

Global observations with information content on water vapor content, ice water content and ice particle size distribution are needed to enhance knowledge of the impact of ice clouds on Earth's weather and climate. These observations may also help to reduce the uncertainty of global climate models. The Tropospheric Water and Cloud Ice (TWICE) microwave radiometer instrument has been designed to perform temperature and humidity sounding of the atmosphere near the 118.75, 183.31 and 380.20 GHz atmospheric absorption lines, as well as to retrieve ice cloud particle size information from radiometric measurements at 240, 310, 670 and 850 GHz. To acquire high-quality data, the TWICE instrument performs end-to-end, on-orbit calibration of all radiometer channels during each scan. The TWICE instrument is designed to fit within the mass, volume and power constraints of the 6U CubeSat platform.

The Tropospheric Water and Cloud ICE (TWICE) millimeter and sub-millimeter radiometer instrument is being developed to enable global observations of upper tropospheric/lower-stratospheric water vapor and ice particle size distribution in clouds. Global observations using the TWICE instrument are critically needed to reduce uncertainties in weather and climate models. A low-noise, power-efficient command and data handling (C&DH) subsystem has been designed and tested to control TWICE data acquisition and other subsystems. Considering the limited power resources available on such platforms, a highly-efficient power regulation board has been designed to minimize power losses and reduce system noise. Furthermore, heavy-ion radiation testing has been performed for some critical commercial-off-the-shelf components to analyze radiation tolerance in low-Earth orbit. The C&DH prototype board meets the functional, noise and size, weight and power (SWaP) requirements for deployment on a 6U -Class satellite.

We introduce a phase calibration scheme for an interferometric frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) to correct range-dependent phase errors in FMCW SAR interferograms. We demonstrate that the receiver filters operating on the FMCW beat frequency signal account for most of the phase mismatch between the different receiver channels. The scheme presented estimates the phase error in each channel. We present results of the scheme for three estimation approaches (curve fitting, joint least squares, and maximum likelihood) for two different phase models. The results are quantified by computing the reduction in spectral energy associated with the phase mismatch. We find that phase error can be reduced by 14 dB using the approach.

In this paper, we investigate the effect of measurement error in platform velocity and attitude on the ATI phase measurement through theoretical analysis and numerical simulations. Our ultimate goal is to determine the maximum motion and attitude measurement error that can be tolerated for airborne ATI SAR measurements.

Global measurements of upper tropospheric/lower-stratospheric water vapor and ice particle size distribution in clouds are critically needed to reduce uncertainties in global weather and climate models. To address this need, the conically scanning Tropospheric Water and Cloud ICE (TWICE) millimeter and submillimeter radiometer instrument is being developed. A low-noise, power-efficient command and data handling (C&DH) subsystem has been designed to control TWICE data acquisition and other subsystems. The C&DH prototype board meets functional, noise and size, weight and power (SWaP) requirements for deployment in a 6U-class satellite. Considering the limited power resources available on such platforms, a highly-efficient power regulation board has been designed to minimize power losses and reduce system noise. Furthermore, all of the components have been tested for radiation tolerance in low-Earth orbit.

The relationship between synthetic aperture radar (SAR) signatures of depth-limited breaking waves and wave height is studied. Wave height is estimated from SAR images using an empirically derived relationship that exploits the azimuthal shift in SAR images associated with moving scatterers. This relationship is derived from in situ measurements rather than from an idealized model of breaking waves as was done in a previous study. We find that the lengths of the SAR signatures are correlated with the observed significant wave height (the correlation coefficient is 0.78) for a range of wave conditions. The relationship between the wave heights and velocity bandwidths from the field data is similar to that between simulated (with a Boussinesq surface wave model) wave heights and velocity ranges (correlation coefficient = 0.82).

Surface flow is estimated from a dual-beam along-track interferometric synthetic aperture radar at the mouth of a tidally-driven estuary. The measurements show strong variation in the surface flow around jetties and seem to be associated with bathymetry. The surface flow estimates compare well with in situ drifter measurements made around the same time.

Techniques to estimate and correct range-dependent phase differences between receivers in an FMCW ATI SAR are studied. Both techniques reproduce the range-dependent phase ripple seem in the ATI interferograms.

We present a technique to extract geophysical parameters of nearshore ocean breaking waves (e.g., wave height, wave velocity) from ATI SAR data. The technique exploits the azimuthal shift induced by moving scatterers in SAR imagery. We find that length of the azimuthal streaks are correlated with breaking wave height (correlation coefficient is 0.78) for a range of wave conditions. We also outline a technique for highlighting breaking waves in SAR imagery using the ATI SAR images.