SFIT4: Line-by-line nonlinear spectral fitting software

SFIT4 is a radiative transfer and atmospheric constituent profile retrieval algorithm for use with spectra recorded in solar absorption and emission across the infrared spectrum. The predecessor of SFIT4 (SFIT & SFIT2) were co-developed over time at NASA Langley, NIWA Lauder NZ and the Univ. of Denver (Chang & Shaw, 1977, Niple, 1980, Goldman et al., 1980, Pougatchev & Rinsland, 1995). The current version of SFIT4 v1.0.18 implements a line-by-line code with 1st order line-mixing and the generalized lineshape profile algorithm pCqSDHC (Ngo, 2013). It is optimized for upwards looking geometry using Fourier Transform Spectrometers spectra. For the retrieval of atmospheric chemical profiles the Optimal Estimation (Rodgers 2000) and Thikonov-Phillips-regularization methodologies are implemented. The raytracing algorithm (FASCATM) is integrated in the code (Smith, et. al., 1978, Gallery, et. al., 1983, Shephard, et. al., 2009).

SFIT4 is one of two standard retrieval codes employed by the NDACC IRWG (NDACC Infrared Working Group) and consequently operationally employed for satellite and model validation, trend evaluation and broad range of atmospheric research purposes.

The SFIT4 retrieval algorithm is designed to work with spectroscopic data from HITRAN (Rothman 2005, Gordon 2017, Gordon 2022) and ATM (Toon 2016, Toon 2017).

A priori input chemical profiles are extracted from WACCM v5, (Gettelman 2019).

The source code can be obtained from the link below or upon request with the principal investigators.