Jamine Lee

MODTRAN5: 2006 update

The MODTRAN5 radiation transport (RT) model is a major advancement over earlier versions of the MODTRAN atmospheric transmittance and radiance model. New model features include (1) finer spectral resolution via the Spectrally Enhanced Resolution MODTRAN (SERTRAN) molecular band model, (2) a fully coupled treatment of auxiliary molecular species, and (3) a rapid, high fidelity multiple scattering (MS) option. The finer spectral resolution improves model accuracy especially in the mid- and long-wave infrared atmospheric windows; the auxiliary species option permits the addition of any or all of the suite of HITRAN molecular line species, along with default and user-defined profile specification; and the MS option makes feasible the calculation of Vis-NIR databases that include high-fidelity scattered radiances. Validations of the new band model algorithms against line-by-line (LBL) codes have proven successful.

Analysis of Hyperion data with the FLAASH atmospheric correction algorithm

A combination of good spatial and spectral resolution make visible to shortwave infrared spectral imaging from aircraft or spacecraft a highly valuable technology for remote sensing of the Earths surface. Many applications require the elimination of atmospheric effects caused by molecular and particulate scattering; a process known as atmospheric correction, compensation, or removal. The Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) atmospheric correction code derives its physics-based algorithm from the MODTRAN4 radiative transfer code. A new spectra; recalibration algorithm, which has been incorporated into FLAASH, is described. Results from processing Hyperion data with FLAASH are discussed.

Speed and accuracy improvements in FLAASH atmospheric correction of hyperspectral imagery

Abstract. Remotely sensed spectral imagery of the earth’s surface can be used to fullest advantage when the influence of the atmosphere has been removed and the measurements are reduced to units of reflectance. Here, we provide a comprehensive summary of the latest version of the Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes atmospheric correction algorithm. We also report some new code improvements for speed and accuracy. These include the re-working of the original algorithm in C-language code parallelized with message passing interface and containing a new radiative transfer look-up table option, which replaces executions of the MODTRAN® model. With computation times now as low as ~10  s per image per computer processor, automated, real-time, on-board atmospheric correction of hyper- and multi-spectral imagery is within reach.

MODTRAN5: a reformulated atmospheric band model with auxiliary species and practical multiple scattering options

The MODTRAN5(1a, in press) radiation transport (RT) model is a major advancement over earlier versions of the MODTRAN(tm) atmospheric transmittance and radiance model. New model features include (1) finer spectral resolution via the Spectrally Enhanced Resolution MODTRAN(tm) (SERTRAN) molecular band model, (2) a fully coupled treatment of auxiliary molecular species, and (3) a rapid, high fidelity multiple scattering (MS) option. The finer spectral resolution improves model accuracy especially in the mid- and long-wave infrared atmospheric windows; the auxiliary species option permits the addition of any or all of the suite of HITRAN molecular line species, along with default and user-defined profile specification; and the MS option makes feasible the calculation of Vis-NIR databases that include high-fidelity scattered radiances.

Measurement of molecular concentrations and line parameters using line-locked second harmonic spectroscopy with an AlGaAs diode laser

The technique of line-locked wavelength modulation with 2f detection is applied to the measurement of water vapor concentration and absorption line parameters by using an 820-nm AlGaAs communications diode laser. Measurements of the 2f signal as a function of the modulation amplitude yield accurate concentrations and line parameters over a pressure range of an order of magnitude and half-widths from 0.02 to 0.15 cm(-1). Usingtwo different spectral lines, we determined concentrations and line parameters with 1% precision, and the absolute accuracy of the line parameters is 3% or better. The results have been used to calculate calibration curves for a diode laser humidity monitor.

DMD-based adaptive spectral imagers for hyperspectral imagery and direct detection of spectral signatures

Dispersive transform spectral imagers with both one- and two-dimensional spatial coverage have been demonstrated and characterized for applications in remote sensing, target classification and process monitoring. Programmable spatial light modulators make it possible to adjust spectral, temporal and spatial resolution in real time, as well as implement detection algorithms directly in the digitally controlled sensor hardware. Operating parameters can be optimized in real time, in order to capture changing background and target evolution. Preliminary results are presented for short wave, mid-wave, and long-wave infrared sensors that demonstrate the spatial and spectral versatility and rapid adaptability of this new sensor technology.

Diode laser measurements of temperature-dependent line parameters for water vapor near 820 nm

Abstract Air- and self-broadening coefficients and relative line strenghts for 8–10 low-J lines in the (2 1 1) vibrational band of water vapor have been accurately measured over the T = 330–540 K range using an 817–824 nm GaAlAs diode laser. The technique of wavelength modulation with third-harmonic line locking and second-harmonic detection was used to derive the line parameters with accuracies of several percent from measurements with absorptivities as low as 2 x 10 -3 . The linewidths and temperature coefficients are in good agreement with theoretical calculations and with recent measurements in the (2 2 1) and (3 0 1) bands. Absolute line strenghts have been derived from measurements on two of the lines and are found to be 21 ±4% higher than the values listed in the 1991 HITRAN compilation.

Improvements in Aerosol Retrieval for Atmospheric Correction

First-principles atmospheric correction that converts Visible-NIR-SWIR spectral imagery to surface reflectance requires an estimate of the scene visibility / aerosol optical depth. This paper describes aerosol upgrades to FLAASH, a first-principles atmospheric correction algorithm developed by Spectral Sciences, Inc. and the US Air Force Research Laboratory. FLAASH utilizes an automated band ratio method for retrieving an average scene visibility from dark pixels. The visibility estimate is combined with a MODTRANTM aerosol representation to describe the atmosphere. Recent FLAASH upgrades improve both visibility retrieval and atmospheric correction accuracy. These result in better handling of highly off-nadir viewing geometries, high aerosol optical depths and sensors lacking infrared spectral channels.

TEMPERATURE AND TEMPERATURE PROFILE MEASUREMENTS IN THE COMBUSTOR FLOWPATH USING STRUCTURED EMISSION THERMOGRAPHY

Structured Emission Thermometry (SET) is a new optical technique for deriving temperature and species concentrations in high-temperature regions of a combustor flow-path from measurements of water and soot emission spectra in the 1 micron region. A prototype instrument has been built for gas- and liquid-fuel combustors with temperatures ranging from 1400–2500K (2100–4000F). This instrument can be used for test stand instrumentation and routine monitoring in fixed installations. With further evolution, the technique may be suitable for an aircraft engine control system. The emissions are measured along narrow lines of sight using small, simple passive fiber probes placed at a short standoff distance from the hot gas flow-path. With proper placement of multiple probes, data may be collected over overlapping lines of sight and inverted to produce a low-resolution spatial map of the temperature and emitter density in the flow-path. In this work, we describe a series of combustor measurements, including cross-validation measurements in a well-controlled laboratory flame and measurements in combustor test stands. Both line-of-sight measurements and reconstructed temperature profiles are presented and discussed.Copyright

Programmable Adaptive Spectral Imagers for Mission-Specific Application in Chemical/Biological Sensing

An innovative passive standoff system for the detection of chemical/biological agents is described. The spectral, temporal and spatial resolution of the data collected are all adjustable in real time, making it possible to keep the tradeoff between the sensor operating parameters at optimum at all times. The instrument contains no macro-scale moving parts and is therefore an excellent candidate for the development of a robust, compact, lightweight and low-power-consumption sensor. The design can also serve as a basis for a wide variety of spectral instruments operating in the visible, NIR, MWIR, and LWIR to be used for surveillance, process control, and biomedical applications.