Smith, Mark William | Search NASA

DOE OSTI2012

Modeling, sensor design, and performance predictions for gas filter correlation radiometers

Gas filter correlation (GFC) radiometry is a technique for detecting and measuring a specific gas or a small suite of gases. The GFC approach combines extremely high spectral resolution with high optical throughput (or etendue) while avoiding the stringent alignment and mechanical stability requirements imposed by interferometric measurements. The GFC approach is well matched to staring imagers and is very efficient in terms of data volume and bandwidth. A primary limitation to GFC for atmospheric remote sensing is the fact that it works best with gases that have strong absorption features but that are present in small concentrations. This report describes a software model that was developed to predict the performance of GFC sensors. This report presents a design for an airborne GFC sensor and predicts the ability of this sensor and a hypothetical satellite sensor to measure methane in the atmosphere.

Mercier, Jeffrey Alan↗

DOE OSTI2010

A fast partial Fourier transform (FPFT) for data compression and filtering.

A discrete Fourier transform (DFT) or the closely related discrete cosine transform (DCT) is often employed as part of a data compression scheme. This paper presents a fast partial Fourier transform (FPFT) algorithm that is useful for calculating a subset of M Fourier transform coefficients for a data set comprised of N points (M < N). This algorithm reduces to the standard DFT when M = 1 and it reduces to the radix-2, decimation-in-time FFT when M = N and N is a power of 2. The DFT requires on the order of MN complex floating point multiplications to calculate M coefficients for N data points, a complete FFT requires on the order of (N/2)log{sub 2}N multiplications independent of M, and the new FPFT algorithm requires on the order of (N/2)log{sub 2}M + N multiplications. The FPFT algorithm introduced in this paper could be readily adapted to parallel processing. In addition to data compression, the FPFT algorithm described in this paper might be useful for very narrow band filter operations that pass only a small number of non-zero frequency coefficients such that M << N.

99 GENERAL AND MISCELLANEOUS↗