Ron Muellerschoen

UAVSAR: a new NASA airborne SAR system for science and technology research

NASAs Jet Propulsion Laboratory is currently building a reconfigurable, polarimetric L-band synthetic aperture radar (SAR), specifically designed to acquire airborne repeat track SAR data for differential interferometric measurements. Differential interferometry can provide key deformation measurements, important for studies of earthquakes, volcanoes and other dynamically changing phenomena. Using precision real-time GPS and a sensor controlled flight management system, the system will be able to fly predefined paths with great precision. The expected performance of the flight control system will constrain the flight path to be within a 10 m diameter tube about the desired flight track. The radar will be designed to be operable on a UAV (unpiloted aerial vehicle) but will initially be demonstrated on a on a NASA Gulfstream III. The radar will be fully polarimetric, with a range bandwidth of 80 MHz (2 m range resolution), and will support a 16 km range swath. The antenna will be electronically steered along track to assure that the antenna beam can be directed independently, regardless of the wind direction and speed. Other features supported by the antenna include elevation monopulse and pulse-to-pulse re-steering capabilities that will enable some novel modes of operation. The system will nominally operate at 45,000 ft (13800 m). The program began as an Instrument Incubator Project (IIP) funded by NASA Earth Science and Technology Office (ESTO).

First deformation results using the NASA/JPL UAVSAR instrument

The UAVSAR instrument, employing an L-band actively electronically scanned antenna, had its genesis in NASAs ESTO Instrument Incubator Program and after 4 years of development has begun collecting science data for investigators. System design was motivated by solid Earth applications where repeat pass radar interferometry can be used to measure subtle deformation of the surface, however flexibility and extensibility to support other applications were also major design drivers. In fact a Ka-band single-pass radar interferometer for making high precision topographic maps of ice sheets was developed and tested based to a large extent on components of the UAVSAR L-band radar. By designing the radar to be housed in an external unpressurized pod, it has the potential to be readily ported to many platforms. Initial testing is being carried out with the NASA Gulfstream III aircraft, which has been modified to accommodate the radar pod and has been equipped with precision autopilot capability developed by NASA Dryden Flight Research Center. With this the aircraft can fly within a 10 m diameter tube on any specified trajectory necessary for repeat-pass radar interferometric applications. To maintain the required pointing for repeat-pass interferometric applications we have employed an actively scanned antenna steered using INU measurement data. This paper presents a brief overview of some of the initial deformations made by the UAVSAR instrument.

The UAVSAR instrument: Description and first results

The UAVSAR instrument, employing an L-band actively electronically scanned antenna, had its genesis in the ESTO Instrument Incubator Program and after 3 years of development has begun collecting engineering and science data. System design was motivated by solid Earth applications where repeat pass radar interferometry can be used to measure subtle deformation of the surface, however flexibility and extensibility to support other applications were also major design drivers. In fact a Ka-band single-pass radar interferometer for making high precision topographic maps of ice sheets is being developed based to a large extent on components of the UAVSAR L-band radar. By designing the radar to be housed in an external unpressurized pod, it has the potential to be readily ported to many platforms. Initial testing is being carried out with the NASA Gulfstream III aircraft, which has been modified to accommodate the radar pod and has been equipped with precision autopilot capability developed by NASA Dryden Flight Research Center. With this the aircraft can fly within a 10 m diameter tube on any specified trajectory necessary for repeat-pass radar interferometric applications. To maintain the required pointing for repeat-pass interferometric applications we have employed an actively scanned antenna steered using INU measurement data. This paper presents a brief overview of the radar instrument and some of the first imagery obtained from the system.

Status of a UAVSAR designed for repeat pass interferometry for deformation measurements

NASAs Jet Propulsion Laboratory is currently implementing a reconfigurable polarimetric L-band synthetic aperture radar (SAR), specifically designed to acquire airborne repeat track interferometric (RTI) SAR data, also known as differential interferometric measurements. Differential interferometry can provide key deformation measurements, important for the scientific studies of earthquakes and volcanoes. Using precision real-time GPS and a sensor controlled flight management system, the system will be able to fly predefined paths with great precision. The expected performance of the flight control system will constrain the flight path to be within a 10 m diameter tube about the desired flight track. The radar will be designed to operate on a UAV (unpiloted aerial vehicle) but will initially be demonstrated on a minimally piloted vehicle (MPV), such as the Proteus built by scaled composites or on a NASA Gulfstream III. The radar design is a fully polarimetric with an 80 MHz bandwidth (2 m range resolution) and 16 km range swath. The antenna is an electronically steered along track to assure that the actual antenna pointing can be controlled independent of the wind direction and speed. Other features supported by the antenna include an elevation monopulse option and a pulse-to-pulse resteering capability that will enable some novel modes of operation. The system will nominally operate at 45,000 ft (13800 m). The program began out as an Instrument Incubator Project (IIP) funded by NASA Earth Science and Technology Office (ESTO).

UAVSAR: New NASA Airborne SAR System for Research

NASAs Jet Propulsion Laboratory is currently building a reconfigurable, polarimetric L-band synthetic aperture radar (SAR), specifically designed to acquire airborne repeat track SAR data for differential interferometric measurements. Differential interferometry can provide key deformation measurements, important for studies of earthquakes, volcanoes, and other dynamically changing phenomena. Using precision real-time GPS and a sensor controlled flight management system, the system will be able to fly pre-defined paths with great precision. The expected performance of the flight control system will constrain the flight path to be within a 10 m diameter tube about the desired flight track. The radar will be designed to be operable on a Unpiloted Arial Vehicle (UAV) but will initially be demonstrated on a NASA Gulfstream III. The radar will be fully polarimetric, with a range bandwidth of 80 MHz (2 m range resolution), and will support a 16 km range swath. The antenna will be electronically steered along track to assure that the antenna beam can be directed independently, regardless of the wind direction and speed. Other features supported by the antenna include elevation monopulse and pulse-to-pulse re-steering capabilities that will enable some novel modes of operation. The system will nominally operate at 45,000 feet (13,800 m). The program began as an Instrument Incubator Project (IIP) funded by NASA Earth Science and Technology Office (ESTO).

Residual motion estimation for UAVSAR: Implications of an electronically scanned array

The UAVSAR instrument, employing an L-band actively electronically scanned antenna, had its genesis in the ESTO Instrument Incubator Program and after 3 years of development has begun collecting engineering and science data. System design was motivated by solid Earth applications where repeat pass radar interferometry can be used to measure subtle deformation of the surface, however flexibility and extensibility to support other applications were also major design drivers. In order to make geophysically useful repeat pass interferometric measurements it is necessary to reconstruct the repeat pass baseline with millimeter accuracy, however onboard motion metrology systems only achieve 5–15 cm accuracy. Thus it is necessary to recover the residual motion from the data itself. Algorithms for recovering the motion based on along-track offsets between the repeat pass interferometric pair of images were described in [3], [1] and [4]. Later these techniques were extended to use azimuth subbanded differential interferograms in [5]. This paper provides a derivation for the formula for the along-track offsets (or corresponding the subbanded differential phase), i.e. the relative displacement between two SAR images in a interferometric pair in the along track direction, as a function of baseline for systems employing an electronically scanned antenna. The standard formula for systems not employing electronically scanned antenna for the along-track offsets, Δs, has the form in given equation where bc is the cross-track baseline, bh is the vertical baseline, θℓ is the look angle, θaz is the azimuth or squint angle, ρ is the range and d = 1 for left looking systems and d = −1 for right looking systems. A key feature of this formula is the along-track offsets only range dependency is from the derivatives of the baseline with respect to along-track position. In the electronically scanned case this in no longer true and an additional range dependency arises that is a function of the electronic steering angle.

UAV-based L-band SAR with precision flight path control

NASAs Jet Propulsion Laboratory is currently implementing a reconfigurable polarimetric L-band synthetic aperture radar (SAR), specifically designed to acquire airborne repeat track interferometric (RTI) SAR data, also know as differential interferometric measurements. Differential interferometry can provide key displacement measurements, important for the scientific studies of Earthquakes and volcanoes1. Using precision real-time GPS and a sensor controlled flight management system, the system will be able to fly predefined paths with great precision. The radar will be designed to operate on a UAV (Unmanned Arial Vehicle) but will initially be demonstrated on a minimally piloted vehicle (MPV), such as the Proteus build by Scaled Composites. The application requires control of the flight path to within a 10 m tube to support repeat track and formation flying measurements. The design is fully polarimetric with an 80 MHz bandwidth (2 m range resolution) and 16 km range swath. The antenna is an electronically steered array to assure that the actual antenna pointing can be controlled independent of the wind direction and speed. The system will nominally operate at 45,000 ft. The program started out as a Instrument Incubator Project (IIP) funded by NASA Earth Science and Technology Office (ESTO).

Some first polarimetric-interferometric multi-baseline and tomographic results at Harvard forest using UAVSAR

Quantification of the various components of the carbon cycle budget is key to improved climate modeling and projecting anthropogenic affects on climate in the future. Estimating the levels of above ground biomass contained in the worlds forests that comprise 86% of the planets above ground carbon and monitoring the rate of change to these standing stocks resulting from both natural and anthropogenic disturbances is necessary to solving the carbon cycle sink. Remote sensing is the only viable means of obtaining a global inventory of forest biomass at the hectare scale. The most promising means of obtaining remotely sensed biomass measurements involve using either lidar or radar measurements of vegetation structure coupled with allometric relationships. We have collected repeat-pass L-band fully polarimetric radar data at multiple spatial and temporal baselines to investigate the tree height and structure measurements using polarimetric interferometry techniques. This paper will discuss this experiment and comparison with lidar data.

Real-time autonomous disturbance detection and monitoring system with L-band UAVSAR

We developed an autonomous disturbance detection and monitoring system with imaging radar that combines the unique capabilities of imaging radar with high throughput onboard processing technology and onboard automated response capability based on specific science algorithms. This smart sensor development leverages off recently developed technologies in real-time onboard synthetic aperture radar (SAR) processor and onboard automated response software as well as science algorithms previously developed for radar remote sensing applications. In this project, we use a high rate data interface to ingest NASApsilas UAVSAR data and compute SAR imagery in real-time complete with motion compensation and antenna beam steering capabilities. NASApsilas UAVSAR is a compact, L-band 80 MHz bandwidth, fully polarimetric radar. It is designed for repeat-pass InSAR and has had engineering flights in 2007 and successful science data collections in 2008. The fidelity of the onboard SAR processor is tuned by implementing polarimetric calibration capabilities. Science algorithms are implemented for detecting and monitoring fire disturbances over the US forests. We additionally developed artificial intelligence for decision-making, and adapted existing onboard activity re-planning and execution software to interface with the UAVSAR radar controller. The product of this development is a prototype closed loop smart sensor.