William Hayden Smith

Imaging interferometer for terrestrial remote sensing

A prototype imaging interferometer called DASI (digital array scanned interferometer) is under development at our laboratories. Our objective is to design an instrument for remote sensing of Earths atmosphere and surface. This paper describes the unusual characteristics of DASIs which make them promising candidates for ground and aircraft-based terrestrial measurements. These characteristics include superior signal-to-noise, design simplicity and compactness, relative to dispersion based imaging spectrometers. Perhaps one of the most notable features of DASIs is their ability to acquire an entire interferogram simultaneously without any moving optical elements. We also describe selected laboratory and ground based field measurements using the prototype DASI. A CCD detector array was placed at the DASI detector plane for wavelength coverage from 0.4 to 1.0 micrometers . A NICMOS MCT detector was used for coverage from 1.1 to 2.2 micrometers . The DASI was configured to have a spectral resolution of about 300 cm-1, a spatial field of view of 5 degrees, and a constant number of transverse spatial elements (detector dependent) for each exposure frame. Frame exposure rates were up to 0.6 Hz with the potential to achieve 5 Hz. Image cube measurements of laboratory targets and terrestrial scenes were obtained by multiple frame scanning over the field of view. These data sets reveal the potential science yields from obtaining simultaneous high resolution spatial and spectral information.

Early Career Development in Academic Pediatrics of Participants in the APS-SPR Medical Student Research Program

To recruit and train the next generations of pediatric clinician-scientists, the American Pediatric Society and Society for Pediatric Research initiated a program in 1991 to support medical students with interests in research and pediatrics to conduct research at institutions other than their respective medical schools. Since 1991, the American Pediatric Society-Society for Pediatric Research Medical Student Research Program (MSRP) has funded 732 of 2209 applicants from 132 US or Canadian medical schools for 8–12 wk of research under the direction of experienced investigators. PubMed-attributable publications tabulated in 2001 for MSRP applicants through 2000 indicated that participants had published more actively than had nonparticipant applicants. Male nonparticipants exhibited greater publication activities than did female nonparticipants, but female and male participants published equally. Of all MSRP participants between 1991 and 1996, as of 2008, 36% were in pediatrics, and a remarkable 29% were in academic pediatrics.

Spectrum estimation from quantum-limited interferograms

A quantitative model for interferogram data collected in a quantum-limited hyperspectral imaging system is derived. This model accounts for the geometry of the interferometer, the Poisson noise, and the parameterization of the mean of the noise in terms of the autocorrelation function of the incident optical signal. The Crame/spl acute/r-Rao bound on the variance of unbiased spectrum estimates is derived and provides an explanation for what is often called the multiplex disadvantage in interferometer-based methods. Three spectrum estimation algorithms are studied: maximum likelihood via the expectation-maximization (EM) algorithm, least squares (LS), and the fast Fourier transform (FFT) with data precorrection. Extensive simulation results reveal advantages and disadvantages with all three methods in different signal-to-noise ratio (SNR) regimes.

Wilderness Medical Society Practice Guidelines for the Treatment of Acute Pain in Remote Environments

The Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the management of pain in austere environments. Recommendations are graded based on the quality of supporting evidence as defined by criteria put forth by the American College of Chest Physicians.

Imaging interferometry for terrestrial remote sensing: digital array scanned interferometer instrument developments

An imaging spectrometer concept called digital array scanned interferometry (DASI) is being explored in our laboratories for terrestrial remote sensing applications. The essence of DASI operation is that interferograms are resolved spatially over one coordinate at the detector plane, and spatial information is obtained over the orthogonal coordinate. In this paper we focus on recent developments for approaching the fundamental capabilities of the DASIs performance, specifically the signal-to-noise ratio. We also describe selected land observations acquired from an airborne DASI operating in the 4550-9090 cm-1 (1.1-2.2 micrometers ) spectral region with a spectral resolution of 266 cm-1.

Computational hyperspectral interferometry for studies of brain function: proof of concept.

Hyperspectral interferometric microscopy uses a unique combination of optics and algorithm design to extract information. Local brain activity rapidly changes local blood flow and red blood cell concentration (absorption) and oxygenation (color). We demonstrate that brain activity evoked during whisker stimulation can be detected with hyperspectral interferometric microscopy to identify the active whisker-barrel cortex in the rat brain. Information about constituent components is extracted across the entire spectral band. Algorithms can be flexibly optimized to discover, detect, quantify, and visualize a wide range of significant biological events, including changes relevant to the diagnosis and treatment of disease.

Estimation of overlapping spectral signatures from hyperspectral data

A new method for spectral unmixing is developed. This method accounts for the nonnegativity of the mixing constants. Preliminary experiments to test the method are reported.

Compensation for optical distortion in Fourier transform spectrometers

A calibration method for determining and correcting the optical distortion in the spectral axis of a Fourier Transform spectrometer is proposed. In our method, a narrowband optical calibration source is used, and the resulting interferogram is treated as a sinusoid which is phase-modulated as a result of the optical distortion. A discrete-time quadrature demodulator is used to determine the phase modulation, and the distortion is then characterized using a third-order polynomial fit to this estimated phase. Correction of interferogram data is accomplished by resampling the discrete data onto a uniform grid in the predistortion space. Our method has been applied to calibration data from the Digital Array Scanned Interferometer (DASI), with excellent results.

Interferometric imagery from a solar powered RPV

Describes the design, integration, and deployment of a compact, high-spectral-resolution imaging interferometer built specifically for use on the Pathfinder solar powered remotely piloted aircraft (RPA) that has been developed under NASAs Environmental Research Aircraft and Sensor Technology (ERAST) program. Emphasis is placed on the engineering challenges associated with RPA instruments, including low power and weight constraints, extreme thermal and pressure environment, and remote operation. Sample data are presented that illustrate the strengths and weaknesses of the composite RPA/scanned interferometer remote sensing system.

Surface reflectance mapping using interferometric spectral imagery from a remotely piloted aircraft

During October 1997, NASAs Environmental Research Aircraft and Sensor Technology (ERAST) Program conducted flight tests of the Pathfinder Remotely Piloted Aircraft (RPA) out of the Pacific Missile Range Facility (PMRF), Kauai (Hawaii). The Pathfinder was a light-weight (=500 lb), solar-powered RPA with an extremely limited (=35 lb) sensor payload capacity. One of the ERAST objectives was to evaluate the feasibility of using such RPA platforms to collect remotely sensed data in support of Earth systems science. A key aspect of this objective was to make simultaneous spectral measurements of a common target using an airborne spectral imager and a ground-based spectrometer. Intercomparison of these results, together with modeling of atmospheric radiative effects, enable the establishment of ground-truth and the verification of the spectral imagers radiometric calibration. The outcome of this calibration exercise is a procedure for deriving the surface albedo for a variety of different regions of the overall scene containing the ground-truth target. A Digital Array Scanned Interferometer (DASI) hyperspectral imager jointly developed by NASA Ames Research Center and and Washington University was selected as the imaging spectrometer payload. Compactness, light weight, low power draw, rugged design and simplicity of operation made the DASI an ideal candidate for this mission.