IASI PCA-based compression package
This IASI pre-processing package comprises two parts which may be used either individually or together.
The first part calculates a covariance matrix, based on a set of training data, from which principal components (PCs) are derived. These PCs may then be used in the second part to noise-filter other spectra such that a reduced set of channels can be used for data assimilation. The second part of the code may either use the PCs calculated in the first part or equivalents from external sources.
The aim with this deliverable is to have a relatively simple, stand-alone piece of code that may be used both to calculate the PCs required and to apply them to new spectra to perform noise filtering.
Input data for Part 1: A training set of full spectral resolution IASI radiances, an estimate of the instrument noise, and the required output channel specification list.
Output data from Part 1: The set of principal components of the input data set.
Input data for Part 2: Full spectral resolution IASI radiances, a set of principal components, the instrument noise assumed when calculating the principal components, and the required output channels specification list.
Output data from Part 2: A noise filtered version of the input spectrum, principal component amplitudes, an estimated error covariance matrix.
In both cases, the form of the input data (e.g. apodised or deapodised spectra, global or local data, channel selection) is irrelevant as this is a statistical exercise and the user needs to ascertain whether the input type is appropriate to their specific application. This is addressed and the user is guided in the documentation for the package.
Bug reports and fixes
None at present
Future plans and applications
- The software is now being used to examine the degree of consistency between PCs derived from real IASI spectra and those derived from simulated spectra. If necessary, the software will be modified in the light of this study. The software will be maintained and further developed on the basis of experience with real IASI observations, and extended to handle CrIS data. Developments in EUMETSAT IASI dissemination policy relating to principal components will be followed.
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