Brian D. Pollard

Direction interval retrieval with thresholded nudging: a method for improving the accuracy of QuikSCAT winds

The SeaWinds scatterometer was developed by NASA JPL, Pasadena, CA, to measure the speed and direction of ocean surface winds. It was then launched onboard the QuikSCAT spacecraft. The accuracy of the majority of the swath and the size of the swath are such that the SeaWinds on QuikSCAT Mission (QSCAT) meets its science requirements despite shortcomings at certain cross-track positions. Nonetheless, it is desirable to modify the baseline processing in order to improve the quality of the less accurate portions of the swath, in particular near the far swath and nadir. Two disparate problems have been identified for these regions. At far swath, ambiguity removal skill is degraded due to the absence of inner beam measurements, limited azimuth diversity and boundary effects. Near nadir, due to nonoptimal measurement geometry, (measurement azimuths approximately 180/spl deg/ apart) there is a marked decrease in directional accuracy even when ambiguity removal works correctly. Two algorithms have been developed: direction interval retrieval (DIR) to address the nadir performance issue and thresholded nudging (TN) to improve ambiguity removal at far swath. The authors illustrate the impact of the two techniques by exhibiting prelaunch simulation results and postlaunch statistical performance metrics with respect to ECMWF wind fields and buoy data.

A Volume-Imaging Radar Wind Profiler for Atmospheric Boundary Layer Turbulence Studies

Abstract This paper describes the turbulent eddy profiler (TEP), a volume-imaging, UHF radar wind profiler designed for clear-air measurements in the atmospheric boundary layer on scales comparable to grid cell sizes of large eddy simulation models. TEP employs a large array of antennas—each feeding an independent receiver—to simultaneously generate multiple beams within a 28° conical volume illuminated by the transmitter. Range gating provides 30-m spatial resolution in the vertical dimension. Each volume image is updated every 2–10 s, and long datasets can be gathered to study the evolution of turbulent structure over several hours. A summary of the principles of operation and the design of TEP is provided, including examples of clear-air reflectivity and velocity images.

A Radar Terminal Descent Sensor for the Mars Science Laboratory mission

The soft-touchdown, “sky-crane” concept employed by the 2009 NASA Mars Science Laboratory mission requires an order-of-magnitude improvement from previous missions in the sensing of vehicle velocity and altitude. This paper describes the development of a new radar “Terminal Descent Sensor” that provides decimeterper-second velocity accuracy while also providing better than 2% range accuracy on six unique beams. This sensor design uses a millimeter-wave center frequency (Ka-band) and pencil beam antennas to achieve the required velocity precision and to overcome the problems that angle-of-arrival errors can cause in velocity reconstruction. Included are discussions of the design concept, driving requirements, hardware architecture, and results from a high fidelity performance simulation.

Next generation millimeter-wave radar for safe planetary landing

Safe, precise landing on planetary bodies requires knowledge of altitude and velocity, and may require active detection and avoidance of hazardous terrain. Radar offers a superior solution to both problems due to its ability to operate at any time of day, through dust and engine plumes, and ability to detect velocity coherently. While previous efforts have focused on providing near term solutions to the safe landing problem, we are designing radar velocimeters and radar imagers for missions beyond the next decade. In this paper we identify the fundamental issues within each approach, at arrive at strawman sensor designs at a center frequency at or around 160 GHz (G-band). We find that a G-band radar velocimeter design is capable of sub-10 cm/s accuracy, and a G-band imager is capable of sub-0.5 degree resolution over a 28 degree field of view. From those designs, we arrive at the key technology requirements for the development of power and low noise amplifiers, signal distribution methods, and antenna arrays that enable the construction of these next generation sensors

The wide swath ocean altimeter: radar interferometry for global ocean mapping with centimetric accuracy

The recent Shuttle Radar Topography Mission (SRTM) has demonstrated the capability for global interferometric topographic mapping with meter level accuracy and 30 meter spatial resolution. The next challenge in radar interferometry is the measurement of ocean topography: the global characterization of ocean mesoscale eddies requires global coverage every 10 days, with centimetric height accuracy, and a spatial resolution of 10-20 km. We have developed an instrument concept that combines a conventional nadir altimeter with a radar interferometer to meet the above requirements. In this paper, we describe the overall mission concept and the interferometric radar design. We also describe several new technology developments that facilitate the inclusion of this instrument on a small, inexpensive spacecraft bus. These include ultralight, deployable reflectarray antennas for the radar interferometer; a novel five frequency feed horn for the radiometer and altimeter; a lightweight, low power integrated three frequency radiometer; and a field programmable gate array-based onboard data processor. Finally, we discuss recent algorithm developments for the onboard date processing, and present the expected instrument performance improvements over previously reported results.

A millimeter-wave phased array radar for hazard detection and avoidance on planetary landers

In this paper, we describe the overall system design for a radar being developed for the NASA Mars Science Laboratory, set to launch in 2009.

Centimetric sea surface height accuracy using the Wide-Swath Ocean altimeter

In this paper, we present error sources and predicted performance of the Wide-Swath Ocean altimeter, an instrument which has been proposed as an experiment for the NASA/CNES Ocean Surface Topography Mission. The data obtained by this instrument will allow the detailed study of ocean mesoscale phenomena, with a space-time resolution which cannot be achieved by a single conventional nadir altimeter.

A G-Band 160 GHz T/R Module Concept for Planetary Landing Radar

In this work, the concept of a G-band transmit/receive (T/R) module centered at 160 GHz was discussed. The design makes use of state-of-the-art G-band MMIC low noise amplifiers and power amplifiers, and a high speed SPDT InGaAs PIN diode switch. The paper reports on the designs, chip results, and the integration concept for a 160 GHz T/R module. The G-band T/R module has applications toward precision altimetry and velocimetry measurements in landing radar, such as in future planetary landers on the surface of Mars

A digital beamforming radar profiler for imaging turbulence in the atmospheric boundary layer

Digital beamforming techniques with adaptive processing have been used for several decades in high performance radar systems to track targets in the presence of jamming. With the availability of inexpensive microwave and digital componentry, these techniques are now practical for non-military applications. The authors have recently developed a 915 MHz digital beamforming radar system, termed the Turbulent Eddy Profiler, designed to resolve atmospheric C/sub n//sup 2/ fluctuations over a three-dimensional volume containing several thousand pixels, with each pixel approximately 30 m on a side. These scales are comparable with large eddy simulations (LES) allowing a comparison of radar-derived structure statistics with those generated by LES.

Methods for testing the Mars Science Laboratory's landing radar

The Mars Science Laboratorys rover named Curiosity successfully landed on Mars on August 6, 2012. One component of the Mars Science Laboratory (MSL) Entry, Descent, and Landing (EDL) system was the Terminal Descent Sensor (TDS) landing radar. In this paper we describe laboratory testing of this radar performed before launch.