The SESAR-LITE (Space Exploration Synthetic Aperture Radar - Lunar Investigations Targeted Experiment) instrument is a compact P-band (70 cm wavelength) polarimetric synthetic aperture radar under development at the NASA Goddard Space Flight Center (GSFC) to measure the surface and upper subsurface of the Moon at full polarimetry and at meter-scale resolution. The radar will use a compact deployable antenna, distributed RF electronics, and multi-channel digital processing system to enable a set of focused mission goals for small payload opportunities. The instrument development leverages proven technology advancements recently developed and demonstrated at NASA GSFC for SESAR (Space Exploration Synthetic Aperture Radar), a flagship version of the instrument that was tailored for larger orbital missions. The development of SESAR-LITE addresses accommodation flexibility on multiple launch vehicle families that require small packages while providing unprecedented surface and subsurface imaging of the Moon as required by NASA’s Artemis program. The goal of this effort is to mature the technology readiness level and to demonstrate the unique features and capabilities of this radar in preparation for upcoming mission opportunities.

Synthetic Aperture Radar acquisitions in nadir (sounding) and side-looking imaging modes are planned for the International-Mars Ice Mapper (I-MIM) orbiter mission to accurately detect ice buried just below the Martian surface. In an effort to gain a comprehensive understanding of the ice detection capability of the I-MIM L-band polarimetric SAR, we developed a Nadir Scattering Radar Model (NRSM), and evaluated it in comparison to a previously implemented Side-looking Radar Scattering Model (SRSM). Together, these Radar Scattering Models (RSMs) permit a thorough evaluation of key radar performance metrics for given sets of radar parameters and Martian surface and shallow subsurface scenarios, and offer new insights into potential depths of detection of buried water ice on Mars.

The use of polarimetric SAR to detect buried water/ice at shallow depths under the Martian surface is quantitatively explored. An electromagnetic model consisting of a dielectric layer that represents the Martian regolith (upper surface layer), with an underlying half space of water/ice, is considered. The top surface of the regolith and the regolith/ice interface are assumed to be rough at radar wavelength scales. It is also assumed that throughout the regolith, small rock particles with arbitrary shapes and prescribed orientation statistics are randomly distributed. Backscattering with co-polarization and cross-polarization from vertical or horizontal polarized waves incidence at L-band frequencies are considered. The Advanced Integral Equation Method (AIEM) is applied to irregular surfaces and the Distorted Born Approximation (DBA) applied to particle scattering and regolith attenuation.

We implemented a 3-D electromagnetic scattering model to gain a better understanding in the observations of L- and P-band radar returns from the multi-layered Martian upper surface layer. The model, based on the Integral Equation Model (IEM) developed by Adrian Fung, treats the Martian regolith (upper 10-meter layer of surface sediments) as an inhomogeneous medium with irregular boundaries, and employs surface and shallow subsurface parameters representative of a variety of Martian terrains. The model is well-suited to study the near-subsurface ice detection capability of the L-band (32 cm wavelength) Synthetic Aperture Radar (SAR) planned for the international Mars Ice Mapping (I-MIM) mission being considered for launching in the late 2020s.

Modern multi-band radiometer imagers are designed trading spatial resolution, spectral coverage, and surface sampling characteristics to optimize science return. In this process, trades must be made to usually under-sample the Earth scene. Care is taken to obtain contiguous 3-dB edge-to-edge coverage, but even so, such a design still aliases high spatial frequency content in the image.

The Space Exploration Synthetic Aperture Radar (SESAR) is a P-band radar instrument for planetary applications being developed at the NASA Goddard Space Flight Center (GSFC). This radar will enable unprecedented surface and near-subsurface measurements of planetary bodies including the Moon, Mars, and asteroids. The radar will measure full polarimetry at meter-scale resolution while featuring a low power, lightweight, beamforming design, specifically developed to meet stringent requirements of planetary instruments. The ongoing prototype development is maturing the SESAR technology for upcoming planetary mission opportunities.

The Space Exploration Synthetic Aperture Radar (SESAR) is a new P-band radar instrument development for planetary applications that will enable unprecedented surface and near-subsurface measurements of planetary bodies including the Moon, Mars, and asteroids. The radar will measure full polarimetry at meter scale resolution, and achieve beam agility through programmable digital beamforming architecture. The radar features a low power, lightweight, modular design, specifically developed to meet stringent launch and operation requirements of planetary instruments. A prototype SESAR system is currently being developed under NASA's MATISSE (Maturation of Instruments for Solar System Exploration) program.

A tri-frequency microwave synthetic aperture radar (SAR), designed for the estimation of snow water equivalent (SWE), was recently developed as part of the SWESARR (Snow Water Equivalent Synthetic Aperture Radar and Radiometer) instrument. The SAR operates at 9.65 GHz, 13.6 GHz, and 17.25 GHz, and at two polarizations (VV, VH), with a nominal bandwidth of 140 MHz. The SAR was first flight tested in December 2018 and later, along with SWESARR's radiometer, participated in the SnowEx science flight campaign in the fall 2019. During these flights, the SAR collected comprehensive data sets of a variety of terrains, including calibration sites where several trihedral corner reflectors had been deployed. Analysis of these data sets indicated the radar performed according to the design specifications.

Radio Frequency Interference (RFI) is a growing problem in Synthetic Aperture Radar (SAR). The choice of operational frequency of remote sensing instruments is dictated by the physics of the parameters that are to be observed. On the other hand, the frequency spectrum becomes more crowded with the increasing demand for wireless services. This requires cohabitation of multiple systems at the same or neighbouring frequency bands. As a result, RFI can introduce artefacts and degrade the derived SAR products. A mitigation of RFI is critical. New removal techniques can be implemented with Digital Beamforming (DBF) radars. In this paper, we present a Pulse and Range-Dependent Time Minimum Variance Distortionless Response (PRDTMVDR) Beamformer. The antenna pattern (AP) is adaptively changed for each pixel based on the inherent imaging geometry of SAR and thus the RFI suppression is improved compared to an AP that is fixed for the pulse duration.

The Space Exploration Synthetic Aperture Radar is a new radar instrument development for planetary applications that will enable unprecedented surface and near-subsurface measurements of planetary bodies including the Moon, Mars, and asteroids. The radar is based on an advanced multiple-input multiple-output (MIMO) architecture that operates in the P-band (70 cm wavelength), measures full polarimetry at meter scale resolution, and achieves beam agility through programmable digital beamforming. The radar is based on a low power, lightweight, modular design approach specifically developed to meet stringent launch and operation requirements of planetary instruments. Prototype SESAR subsystems have been developed and tested, and a recent MATISSE (Maturation of Instruments for Solar System Exploration) proposal was awarded to build and test a functional radar panel.

A new airborne synthetic aperture radar (SAR) system was recently developed for the estimation of snow water equivalent (SWE). The radar is part of the SWESARR (Snow Water Equivalent Synthetic Aperture Radar and Radiometer) instrument, an active passive microwave system specifically designed for the accurate estimation of SWE. The dual polarization (VV, VH) radar operates at three frequency bands (9.65 GHz, 13.6 GHz, and 17.25 GHz), with bandwidths of up to 200 MHz. The radar flew its first flight campaign in November 2019, along with SWESARR's -already operational - radiometer. The radar collected comprehensive data sets over various terrains that show a successful system performance. The instrument is slated to participate in future SnowEx campaigns.

An increasing challenge for P-band Synthetic Aperture Radar (SAR) is Radio Frequency Interference (RFI). RFI results in image distortions and degrades the derived science products. This makes it critical to apply RFI removal techniques to restore the image quality. New advanced techniques can be achieved with Digital Beamforming (DBF) radars such as EcoSAR. In this paper, we present a Range-Dependent Time Minimum Variance Distortionless Response (RDTMVDR) Beamformer and apply it to EcoSAR flight data during post-processing. The antenna pattern (AP) is adaptively changed for each range line which increases the RFI suppression compared to a fixed AP for each pulse. The interferometric image quality is assessed before and after RFI suppression.

SESAR (Space Exploration Synthetic Aperture Radar) is a next generation P-band beamforming radar instrument concept that will enable a new class of observations suitable to meet Decadal Survey science goals for planetary exploration. The radar operates at full polarimetry and fine (meter scale) resolution, and achieves beam agility through programmable transmit waveforms and digital beamforming on receive. The radar is based on a low power, lightweight design approach conceived to meet the stringent planetary instrument requirements. This instrument concept has the potential to provide unprecedented surface and near-subsurface measurements of planetary bodies including the Moon, Mars, and asteroids.

Wideband radar systems operating at L- or P-band encounter an increasing amount of Radio Frequency Interference (RFI). If this RFI is not removed from the obtained radar signal, the quality of extracted science data can be decreased significantly. The removal of RFI can be improved with Digital Beamforming (DBF), a technique that is becoming more important in many radar applications. DBF enables to digitally steer the antenna beam into different directions and to place nulls into the antenna pattern. This technology is implemented in EcoSAR, a synthetic aperture radar (SAR) operating at P-band. Further, in data acquired by EcoSAR in Costa Rica in 2014, the impact of multiple RFI sources can be observed. This gives the opportunity to implement and test new RFI mitigation techniques based on DBF. In this paper, we estimate RFI with DBF and subtract it from EcoSAR data. The method is applied to several acquisitions and results are being presented.

EcoSAR is a single-pass (dual antenna) digital beamforming, P-band radar system that is designed for remote sensing of dense forest structure. Forest structure retrievals require the measurement related to the vertical dimension, for which several techniques have been developed over the years. These techniques use polarimetric and interferometric aspects of the SAR data, which can be collected using EcoSAR. In this paper we describe EcoSAR system in light of its interferometric capabilities and investigate forest structure retrieval techniques.

The Space Exploration Synthetic Aperture Radar (SESAR) is an advanced P-band beamforming radar instrument concept to enable a new class of observations suitable to meet Decadal Survey science goals for planetary exploration. The radar operates at full polarimetry and fine (meter scale) resolution, and achieves beam agility through programmable waveform generation and digital beamforming. The radar architecture employs a novel low power, lightweight design approach to meet stringent planetary instrument requirements. This instrument concept has the potential to provide unprecedented surface and near-subsurface measurements applicable to multiple Decadal Survey Science Goals.

Next Generation Digital Beamforming (DBF) Synthetic Aperture Radar (SAR) is a technological area being pursued at the NASA Goddard Space Flight Center (GSFC). Two such systems - DBSAR-2 and EcoSAR-have been recently developed and tested. The new instruments employ advanced architectures characterized by multi-mode operation, software defined waveform generation, digital beamforming, and configurable radar parameters. The instruments have been developed to support several disciplines in Earth and Planetary sciences. This paper will describe EcoSAR and DBSAR-2 advanced features and report on the latest SAR processing and calibration efforts.

Radio frequency interference (RFI) has strong influence on radar systems, especially for wideband airborne radars operating in the P-band (UHF). EcoSAR is a 435 MHz Synthetic Aperture Radar (SAR) system that employs a wideband digital beamforming architecture for the measurement of science parameters. RFI in EcoSAR measurements, degrades the quality of the SAR data and has to be removed from raw echoes. In this paper, we describe the current methodology used to mitigate RFI with EcoSAR, and provide an example on its performance. We also discuss the advantages and disadvantages of the proposed methods and discuss potential improvements.

Digital Beamforming permits the implementation of non-conventional measurement techniques, which can overcome fundamental limitations of conventional radar systems. In SAR systems, this technique can enable three-dimensional measurements using a single radar platform. A split phase center technique is implemented with NASA's digital beamforming SAR. The technique has the potential to provide volume structure estimates in tall forests and glaciers using a single radar platform.

The second generation Digital Beamforming SAR (DBSAR-2) is a state-of-the-art airborne L-band radar being developed at the NASA Goddard Space Flight Center (GSFC). The instrument employs a 16-channel radar architecture characterized by multi-mode operation, software defined waveform generation, digital beamforming, and configurable radar parameters. The instrument has been design to support several disciplines in Earth and Planetary sciences. This technology seeks to establish the Next Generation SAR as a science instrument while setting a path future airborne and spaceborne SAR missions.

The Eco3D campaign was conducted in the Summer of 2011. As part of the campaign three unique and innovative NASA Goddard Space Flight Center airborne sensors were flown simultaneously: The Digital Beamforming Synthetic Aperture Radar (DBSAR), the Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) and the Cloud Absorption Radiometer (CAR). The campaign covered sites from Quebec to Southern Florida and thereby acquired data over forests ranging from Boreal to tropical wetlands. This paper describes the instruments and sites covered and presents the first images resulting from the campaign.

This paper describes objectives and recent progress on the development of the EcoSAR, a new P-band airborne radar instrument being developed at the NASA/ Goddard Space Flight Center (GSFC) for the polarimetric and interferometric measurements of ecosystem structure and biomass. These measurements support science requirements for the study of the carbon cycle and its relationship to climate change. The instrument is scheduled to be completed and flight tested in 2013.

The Digital Beamforming Synthetic Aperture Radar instrument demonstrated its first polarimetric polarization operation during the Eco-3D flight campaign, on board the NASA P3 aircraft in the summer/fall 2011. The measurements acquired during the campaign are currently being used to demonstrate DBSAR's science utility by providing critical information on vegetation structure needed to estimate vegetation biomass in order to advance our understanding of the carbon cycle.

In this paper we describe the EcoSAR concept, an airborne Polarimetric and Interferometric P- band SAR instrument that will provide unprecedented twoand three dimensional fine scale measurements of terrestrial ecosystem structure and biomass. These measurements are directly traceable to upcoming international radar missions and the National Research Council's Decadal Survey ecosystem measurement requirements.

The EcoSAR instrument is a new concept in Synthetic Aperture Radar for the polarimetric and interferometric measurements of biomass and ecosystem structure. EcoSAR will employ a digital beamforming architecture, a highly capable digital wave form generator and receiver system, and advanced dual-polarization array antennas with an interferometric baseline of 25 m on the NASA P3 aircraft.

The Digital Beamforming Synthetic Aperture Radar (DBSAR) is a state-of-the-art L-band radar that employs advanced radar technology and a customized data acquisition and real-time processor in order to enable multimode measurement techniques in a single radar platform. DBSAR serves as a test bed for the development, implementation, and testing of digital beamforming radar techniques applicable to Earth science and planetary measurements. DBSAR flew its first field campaign on board the National Aeronautics and Space Administration P3 aircraft in October 2008, demonstrating enabling techniques for scatterometry, synthetic aperture, and altimetry.

L-band Imaging Scatterometer (LIS), developed at NASA/Goddard Space Flight Center as part of the RadSTAR initiative, is an airborne imaging radar that combines phased array technology and digital beam forming techniques for the measurement of important scientific parameters. The instrument operates at 1.26 GHz, horizontal polarization, and employs a real-time processor capable of synthesizing multiple beams over a scan range of +/-50 degrees. LIS was flight tested in May 2006 and in January 2007 on board of the NASA P3 aircraft over the Delmarva Peninsula, VA. In this paper we describe the RadSTAR system and present some preliminary analysis of the radar data collected during the test flights.

The RadSTAR initiative merges an interferometric radiometer with a digital beam forming scatterometer, providing Earth surface backscatter and emission measurements. Heretofore these instrument developments have been designed for low flying brown platforms such as the NASA P-3. Commercial-off-the-shelf design materials can be used to inexpensively build antennas that approximate free-space permittivity, enabling remote sensing of soil moisture levels locally using small Unmanned Aerial Vehicles (UAVs). A foam/free-space sandwich can be used to minimize the weight of the dielectric backing structure. This technique enables rapid prototyping with space-grade materials. A low-mass 3-element antenna array of this design is already baselined for a University nano-satellite mission. A light-weighted version of the L-band Imaging Scatterometer (US) radar electronics is being developed for a Small Business Innovative Research (SBIR) program. This lightweight wing antenna has a large potential payoff to NASA. For example, it may enable an active/passive hydrology mission using a fleet of low cost small UAVs. A mesh ground plane can further reduce the overall mass and stowability of the very large antennas required for spaceborne observations at L-Band. The cross track scan success criterion was met at L-Band frequencies for radar and radiometry. That is, we designed and prototyped a wideband antenna patch tunable in this range and additional work is being earned out to improve the cross polarization isolation. Making the present broadband design into arrays will be limited to one dimension due to array spacing and the aspect ratio of the patch elements. A fore and aft Doppler beam synthesis and the US cross-track beam forming concept will be considered for potential application to surface hydrology measurements using these arrays

The L-Band Imaging Scatterometer (LIS) is an airborne radar developed at NASA Goddard Space Flight Center which combines electronic beam steering and digital beamforming allowing the implementation of different scanning techniques. The LIS efforts are part of the RadSTAR initiative intended to develop the technology that will enable a combined radar/radiometer system that jointly uses a single, dual frequency antenna with cross-track scanning capabilities, but no moving parts. The new technology will enable single aperture measurements of important Earth Science Enterprise climate applications such as ocean salinity, soil moisture, sea ice, and surface water among others. The LIS instrument will be flown along with existing NASA Synthetic Thinned Array Radiometers (STAR) in order to prove the concept of coregistered data and to provide a prototype for a spaceborne, single aperture radar/radiometer system.

This paper studies the feasibility of making backscatter measurements from rainfall with the NASA/Microwave Link system at Wallops Island, VA. The research entails the implementation of an FMCW radar at the Link frequencies to enable simultaneous forward and backscatter measurements from rain. The backscatter measurements will be used in conjunction with the forward measurements and the measurements from a ground-based network of disdrometers and rain gauges located under the propagation path to develop new microwave retrieval techniques, and to test established single-frequency and dual-frequency radar retrieval-algorithms relevant to the ongoing TRMM and up coming GPM missions

Although most parameterizations of the drop size distributions (DSD) use the gamma function, there are several advantages to the log-normal form, particularly if we want to characterize the large scale space-time variability of the DSD and rain rate. The advantages of the distribution are twofold: the logarithm of any moment can be expressed as a linear combination of the individual parameters of the distribution; the parameters of the distribution are approximately normally distributed. Since all radar and rainfall-related parameters can be written approximately as a moment of the DSD, the first property allows us to express the logarithm of any radar/rainfall variable as a linear combination of the individual DSD parameters. Another consequence is that any power law relationship between rain rate, reflectivity factor, specific attenuation or water content can be expressed in terms of the covariance matrix of the DSD parameters. The joint-normal property of the DSD parameters has applications to the description of the space-time variation of rainfall in the sense that any radar-rainfall quantity can be specified by the covariance matrix associated with the DSD parameters at two arbitrary space-time points. As such, the parameterization provides a means by which we can use the spaceborne radar-derived DSD parameters to specify in part the covariance matrices globally. However, since satellite observations have coarse temporal sampling, the specification of the temporal covariance must be derived from ancillary measurements and models. Work is presently underway to determine whether the use of instantaneous rain rate data from the TRMM Precipitation Radar can provide good estimates of the spatial correlation in rain rate from data collected in 5(sup 0)x 5(sup 0) x 1 month space-time boxes. To characterize the temporal characteristics of the DSD parameters, disdrometer data are being used from the Wallops Flight Facility site where as many as 4 disdrometers have been used to acquire data over a 2 km path. These data should help quantify the temporal form of the covariance matrix at this site.

Attenuation measurements at 25 and 38 GHz performed with the NASA/TRMM Microwave Link provide information about the drop size distribution (DSD) along the propagation path. Additional path-average measurements along the Link path, such as a third attenuation measurement or the rain rate from well-calibrated raingauges, can provide further DSD information. This paper explores an inversion procedure for determining simultaneously three parameters of a gamma DSD by using three measurements. Also, some preliminary results obtained using Link data are presented.

In an effort to study the drop size distribution (DSD) a state-of-the-art instrument arrangement was deployed on Wallops Island, VA. The instrumentation consisted of a 2.3-km multi-frequency microwave link, three impact disdrometers, and a network of optical and tipping bucket raingauges. A dual-frequency inversion technique was implemented with the link measurements of attenuations at 25 GHz and 38 GHz to estimate the path-average DSD. Concurrently, an X-band, dual-polarization radar, located in the vicinity, collected polarization and reflectivity measurements over the link path. The evaluation of the estimates and measurements generated some preliminary results.

Microwave attenuation measurements at 25 and 38 GHz made on a 2.3-km microwave link are employed to estimate drop size distributions (DSD), rainfall rate, and rainfall accumulation. A theoretical model for the propagation of microwaves in a link system sets forth the basis for the development of a dual-wavelength analytical technique to invert two parameters of a path-average gamma DSD. The DSDs obtained from the technique are evaluated in conjunction with point measurements performed with a 2-D video disdrometer. Additionally, the DSDs yield path-average rainfall rates and rainfall accumulation which are compared with path-average measurements from a network of optical and tipping bucket rain gauges located beneath the link path, and with estimates based on empirical power law relations.