Mark W. James

The hurricane imaging radiometer - an octave bandwidth synthetic thinned array radiometer

The Hurricane Imaging Radiometer (HIRad) is a new airborne sensor that is currently under development. It is intended to produce wide-swath images of ocean surface wind speed and near surface rain rate in hurricanes conditions. HIRad will extend the scientific capabilities and technologies associated with two previous successful airborne microwave radiometers: the real aperture Stepped Frequency Microwave Radiometer (SFMR) and the synthetic aperture Lightweight Rainfall Radiometer (LRR). Both SFMR and HIRad are required to operate over the full C-Band octave in order to estimate precipitation levels experienced in hurricanes without saturation and to penetrate through the precipitation and estimate surface winds. Operation over an octave bandwidth was easily accomplished by the nadir-pointing horn antenna used by SFMR. However, it represents a major technological challenge for the HIRad design because it is a Fourier synthesis imager. Details of how HIRad meets that challenge are described here.

Multi-Frequency Synthetic Thinned Array Antenna for the Hurricane Imaging Radiometer

A C-band four-frequency resonant stacked-patch array antenna is developed for synthetic thinned aperture radiometer measurements of hurricane force wind speeds. This antenna is being integrated into an aircraft instrument referred to as the Hurricane Imaging Radiometer (HIRAD). Details of the antenna design are presented along with antenna performance tests and laboratory measurements using a full-scale prototype array with a subset model of the HIRAD instrument.

Calibration and image reconstruction for The Hurricane Imaging Radiometer (HIRAD)

The Hurricane Imaging Radiometer (HIRAD) is a new airborne passive microwave synthetic aperture radiometer designed to provide wide swath images of ocean surface wind speed under heavy precipitation and, in particular, in tropical cyclones. It operates at 4, 5, 6 and 6.6 GHz and uses interferometric signal processing to synthesize a pushbroom imager in software from a low profile planar antenna with no mechanical scanning. The retrieval algorithm (and the HIRAD instrument itself) is a direct descendant of the nadir-only Stepped Frequency Microwave Radiometer that is used operationally by the NOAA Hurricane Research Division to monitor Tropical Cyclones [1,2]. HIRAD participated in NASAs Genesis and Rapid Intensification Processes (GRIP) mission during Fall 2010 as its first science field campaign. HIRAD produced images of upwelling brightness temperature over a ~70 km swath width with ~3 km spatial resolution. The calibration and image reconstruction algorithms that were used to verify HIRAD functional performance during and immediately after GRIP were only preliminary and used a number of simplifying assumptions and approximations about the instrument design and performance. The development and performance of a more detailed and complete set of algorithms are reported here.

The Hurricane Imaging Radiometer: Present and future

The Hurricane Imaging Radiometer (HIRAD) is an airborne passive microwave radiometer designed to provide high resolution, wide swath imagery of surface wind speed in tropical cyclones from a low profile planar antenna with no mechanical scanning. Wind speed and rain rate images from HIRADs first field campaign (GRIP, 2010) are presented here followed, by a discussion on the performance of the newly installed thermal control system during the 2012 HS3 campaign. The paper ends with a discussion on the next generation dual polarization HIRAD antenna (already designed) for a future system capable of measuring wind direction as well as wind speed.

Beam former development for the NASA Hurricane Imaging Radiometer

The Hurricane Imaging Radiometer (HIRAD) is an airborne passive microwave synthetic aperture radiometer designed to provide high resolution, wide swath imagery of surface wind speed in tropical cyclones from a low profile planar array antenna. This paper will present the array radiometer system concept and summarize its development, including multiple flight tests on NASAs Genesis and Rapid Intensification Processes (GRIP, 2010) and Hurricane and Severe Storm Sentinel (HS3, 2012) campaigns. The paper will focus on the design goals, trades, and approach for the array antenna along-track beam former. The paper presents details of the beam former design, implementation, integration approach, and measured performance. The paper concludes with a description of planned improvements for the next generation dual-polarized HIRAD antenna and the resulting impacts on the beam former design and integration.

Analysis of anechoic chamber testing of the Hurricane Imaging Radiometer

The Hurricane Imaging Radiometer System (HIRAD) is a new airborne passive microwave remote sensor developed to observe hurricanes. HIRAD incorporates synthetic thinned array radiometry technology, which use Fourier synthesis to reconstruct images from an array of correlated antenna elements. The HIRAD system response to a point emitter has been measured in an anechoic chamber. With this data, a Fourier inversion image reconstruction algorithm has been developed. Performance analysis of the apparatus is presented, along with an overview of the image reconstruction algorithm.

Characteristic of a digital correlation radiometer back end with finite wordlength

The performance characteristic of a digital correlation radiometer signal processing back end (DBE) is analyzed using a computer simulator. The particular design studied here corresponds to the airborne Hurricane Imaging radiometer which was jointly developed by the NASA Marshall Space Flight Center, University of Michigan, University of Central Florida and NOAA. Laboratory and flight test data is found to be in accord with the simulation results. Overall design seems to be optimum for the typical input signal dynamic range at the DBE input. It is found that the performance of the digital kurtosis could be improved by lowering the DBE input power level. An unusual scaling between digital correlation channels, observed in the instrument data, is confirmed to be a DBE characteristic.

Calibration of hurricane imaging radiometer C-band receivers

The laboratory calibration of airborne Hurricane Imaging Radiometers C-Band multi-frequency receivers is described here. The method used to obtain the values of receiver front-end loss and injected noise diode temperature is presented along with the expected RMS uncertainty in the final calibration. Internal Warm load was excluded from the calibration due to an apparent anomaly.