Fast reconstruction of hyperspectral radiative transfer simulations by using small spectral subsets: application to the oxygen A band

Abstract

Abstract. Hyperspectral radiative transfer simulations are a versatile tool in remote sensing but can pose a major computational burden. We describe a simple method to construct hyperspectral simulation results by using only a small spectral subsample of the simulated wavelength range, thus leading to major speedups in such simulations. This is achieved by computing principal components for a small number of representative hyperspectral spectra and then deriving a reconstruction matrix for a specific spectral subset of channels to compute the hyperspectral data. The method is applied and discussed in detail using the example of top-of-atmosphere radiances in the oxygen A band, leading to speedups in the range of one to two orders of magnitude when compared to radiative transfer simulations at full spectral resolution.

Evaluation of the operational Aerosol Layer Height retrieval algorithm for Sentinel-5 Precursor: application to O<sub>2</sub> A band observations from GOME-2A

“…When the surface albedo is fitted, 94 % of all GOME-2A pixels had at least one converging retrieval, but in this case, there is a dependence of convergence on starting values (i.e., the fraction of converged runs varied more smoothly between zero and one; not shown). In contrast to reports of multiple minima in the cost function observed in simulation studies (e.g., Hollstein et al, 2012;Sanders and De Haan, 2014), we find for the GOME-2A retrievals that multiple minima hardly seem to occur. Once retrieval converges, it typically converges to the same retrieval solution independent of starting values (see Fig.…”

“…A correlated k-distribution method as described in Hasekamp and Butz (2008) is being implemented. At a later stage, efficient look-up table approaches, such as, for example, described in Hollstein and Lindstrot (2014), may be investigated.…”

“…For example, it has been noted in simulation experiments that the cost function for O 2 A band aerosol retrieval may have multiple local minima (e.g., Fig. 19 in Hollstein et al, 2012;Fig. 6-1 in Sanders and De Haan, 2014).…”

“…These studies include the ones by Geddes and Bösch (2015), Hollstein and Fischer (2014), Sanders and De Haan (2013), Hollstein et al (2012), Hasekamp and Sidans (2009), Siddans et al (2007), Corradini and Cervino (2006), and Gabella et al (1999). Overall, these studies show, among other things, that retrieval precision is typically better when the aerosols are optically thicker or more elevated, or when the solar zenith angle is larger.…”

Retrieving aerosol height from the oxygen A band: a fast forward operator and sensitivity study concerning spectral resolution, instrumental noise, and surface inhomogeneity

“…However, for the case of the oxygen A band, this obstacle can be overcome by exploiting the high correlation of the spectrum with respect to variations of the atmospheric state. Natraj et al (2005) used principal component analysis to speed up the calculation of optical parameters for a radiative transfer model, while Hollstein and Lindstrot (2014) presented an approach based on principal component analyses, which can speed up the population of the lookup table by one or more orders of magnitude. Following the latter approach, a higher speedup is achieved for larger lookup tables.…”