FPGA development for measuring differential phase in real time

Technology assessment and proof of concept prototypes are necessary first step before any new concept and idea can be deployed as a fully proved on-board system. In this approach a radar cross-track interferometer has been constructed along with an integrated digital processing system capable of monitoring temperature and other operating conditions in order to design and test a new generation of radar systems with higher resolution level and a wider swath. Cross-track interferometry is a remote sensing technique that relays on the measurement of phase difference between two data channels to infer characteristics about the target being observed. This type of radars are primarily sensitive to phase and changes in the transmitter characteristics where small differences in temperature can affect the overall performance of the system. Particularly, this thesis is based on the RF receive system of a radar that operates at a frequency of 35.75 GHz (wavelength of 8.4 mm). High frequency means that small fluctuations on the temperature in the two receive channels will manifest themselves as changes in the electrical path length. In this instance, phase differences not related with the measured topographic height will appear, possibly lading to significantly- increased error in the overall system. To address the thermally-induced phase error issue, an adaptive digital receive system have been implemented into a Filed-Programmable Gate Array (FPGA) capable, not just, of measuring and monitoring continuously the phase but also identifying the accuracy of the RF front-end's performance as a function of temperature and compensate these thermally-induced errors in real time. The complete system, the combination of RF and the adaptive digital receive system has been designed and constructed as part of the National Aeronautics and Space Administration (NASA) Surface Water Ocean Topography (SWOT) initiative.L'avaluació tecnològica i la prova de prototips conceptuals és el pas previ necessari per l'implementació final del disseny en un sistema. Seguint aquest enfocament s'ha dissenyat una primera versió d'un radar cross-track interferometer, el qual incorpora un sistema de processat digital integrat capaç de controlar les fluctuacions de temperatura sobre el hardware del sistema de recepció RF i altres condicions de funcionament del sistema. Cross-track interferometry és una tècnica de teledetecció basada en la mesura de la difer ència de fase entre dos canals de dades per inferir característiques de l'objectiu. Aquest tipus de tècnica és principalment sensible a la tempreatura, on petites variacions d'aquesta en l'etapa de transmissió o recepció poden provocar canvis en la mesura de fase i el rendiment global del sistema. En particular, aquesta tesi es basa en l'etapa de recepció RF d'un radar que opera a freqüència 35,75 GHz (longitud d'ona de 8,4 mm). El funcionament a freqüències elevades provoca que, petites fluctuacions de temperatura en l'etapa de recepció del senyal, es manifestin com canvis en la longitud del camí elèctric. En aquest cas, la diferència de fase no és deguda a l'açada topogràfica del terreny, provocant un increment significatiu en l'error sobre tot el sistema global. Per abordar aquest problema s'ha dissenyat un sistema adaptatiu digital implementat sobre una Filed-Programmable Gate Array (FPGA) capaç, no tant sols de mesurar i monitoritzar la fase sinò també de compensar en temps real els errors sobre aquesta produïts per les fluctuacions de temperatura. El sistema complet, la combinació del subsistema RF i el subsistema de recepciò digital adaptable ha estat dissenyat i construït com a part del projecte Surface Water Ocean Topography (SWOT) iniciativa de la National Aeronautics and Space Administration (NASA)

Design and Development of a Ka-band Interferometer for Cryospheric Applications

Topographic maps of the earth are essential to geographic and earth science studies. In particular, mapping and estimating physical parameters of the earth’s water and ice cover are critical to global climate studies. Among these, snow, ocean and fresh water topography, snow wetness and water equivalent are of immediate interest to the scientific community. Challenges in the instrument development and deployment posed by these required measurements are twofold. Firstly, these measurements are required to have global coverage, yet maintain stringent spatial resolution and accuracy margins. Secondly, snow topography measurement requires minimal electromagnetic wave penetration through snow, hence requiring the use of millimeter-wave frequency radars. While having the advantage of smaller and lighter structures, instruments at millimeter-wave frequencies are difficult to design, evaluate and deploy due to their mechanical and electric precision requirements. This thesis presents the design, development, detailed evaluation and first deployment of a Ka-band interferometer. An overview of the theory of interferometric mapping is presented including a discussion on instrument sensitivity and accuracy. Based in this theory, a geometric and hardware configuration for a rooftop deployment is arrived at. Detailed design and evaluation of the radar receiver is documented. Lastly first results from a rooftop and ground-based deployment are presented

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

NASA’s 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 Arial 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)

Summaries of the Sixth Annual JPL Airborne Earth Science Workshop

The Sixth Annual JPL Airborne Earth Science Workshop, held in Pasadena, California, on March 4-8, 1996, was divided into two smaller workshops:(1) The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) workshop, and The Airborne Synthetic Aperture Radar (AIRSAR) workshop. This current paper, Volume 2 of the Summaries of the Sixth Annual JPL Airborne Earth Science Workshop, presents the summaries for The Airborne Synthetic Aperture Radar (AIRSAR) workshop

Application of Satellite-Derived Wind Profiles to Joint Precision Airdrop System (JPADS) Operations

The Joint Precision Airdrop System has revolutionized military airdrop capability, allowing accurate delivery of equipment and supplies to smaller drop zones, from higher altitudes than was previously possible. This capability depends on accurate wind data which is currently provided by a combination of high-resolution forecast models and GPS dropsondes released in the vicinity of the dropzone shortly before the airdrop. This research develops a windprofiling algorithm to derive the needed wind data from passive IR satellite soundings, eliminating the requirement for a hazardous dropsonde pass near the drop zone, or allowing the dropsonde to be dropped farther from the dropzone. Atmospheric temperature measurements made by the Atmospheric Infrared Sounder (AIRS) onboard the polar-orbiting Aqua satellite are gridded and filtered to create a three-dimensional temperature field surrounding a notional airdrop objective area. From these temperatures, pressure surfaces are calculated and geostrophic and thermal wind direction and magnitude are predicted for 25 altitudes between the surface and 500 mb level. These wind profiles are compared to rawinsonde measurements from balloon releases near the notional airdrop location and time of the satellite sounding. The validity of the satellite-derived wind profile is demonstrated at higher altitudes, but this method does not consistently predict wind velocity within the boundary layer. Future research which better accounts for surface friction may improve these results and lead to the single-pass airdrop capability desired by Air Mobility Command

Investigation of developments in interferometric synthetic aperture radar until 1994

Bibliography: p. 149-155.This thesis examines the topic of Synthetic Aperture Radar Interferometry in a historical perspective, tracing its development from its beginnings in the 1960s up until May 1994. Applications are listed and airborne and spaceborne implementations reviewed. The underlying theory of interferometry is explained, including a discussion of error sources, and a simulation for point targets is documented to illustrate the interferometric processing steps. The application of the SASAR VHF SAR system to interferometric operation is examined analytically