Details about the generation of m-factors are given in a corresponding Technical Note (Bramstedt, 2008).
SCIAMACHY long-term monitoring results based on partly calibrated Level 0 data are also available.
126.96.36.199 Short-Term Concept
The m-factor impact on polarization correction is neglected within the short–term solution.
The m–factors are provided by an external database, which than can be applied by a modified Level 1b-1c applicator. Advantages of this approach are:
Only the m-factors describing the degradation of the science channels are needed here; the PMD m-factors are set to 1.
188.8.131.52 Long-Term Concept
On long-term, a full set of m-factors including PMDs can be set up. For this concept, changes of the Level 0-1b processor are necessary. The m-factors are included in the Level 1 product and cannot be switched off, if polarization correction or absolute radiometric calibration is needed. Advantage of this approach is full consistency for reprocessed products.
6.2.5 Algorithm Baseline Documentation
The algorithm baseline documentation consists of a collection of documents that together give a complete specification of the data processor. The most relevant for the user are:
6.2.6 Data Format Description
SCIAMACHY Level 1b products follow the generalized ENVISAT product structure consisting of ASCII and binary structures. A Level 1b product includes headers (MPH, SPH), calibration data sets which are constant for the entire product, the so-called Global Annotation Data Sets (GADS), Annotation Data Sets varying over time (ADS) and several Measurement Data Sets (MDS) for the different viewing modes.
The Main Product Header (MPH) and the Specific Product Header (SPH) are ASCII structures of a fixed number of bytes. The Main Product Header (MPH) identifies the product and its main characteristics: product identification, data acquisition, processing details, etc. The Specific Product Header (SPH) contains information specific to the whole product such as start and stop times and location, summary of the number of states, also with Data Set Descriptors (DSDs) which describe individual Data Sets (DSs) within the product.
The Data Sets (DSs) contain the actual data of interest and may be Measurement Data Sets (MDS), Annotation Data Sets (ADS) or Global Annotation Data Sets (GADS). Data Sets are in mixed-binary format and consist of one or more Data Set Records (DSRs) each.
The measurement data sets (MDSs) include the raw signal values of the array detectors and geolocation information for nadir, limb and occultation measurements.
The different global annotation data sets (GADS) include leakage current and noise characteristics,pixel-to-pixel gain and Etalon parameters, spectral and radiometric calibration parameters, sun reference spectra and the polarization sensitivity parameters and errors on the Key Data.
The time dependent annotation data sets (ADS) include information about the sequence ofstates, the PMD and auxiliary data packets of the level 0 data and optionally a set of newly calculatedin-flight calibration parameters if the corresponding measurements are present in the level 0 data. More details regarding the product structure are given in the SCIAMACHY Product Specification document (Volume 15) and in the SCIAMACHY Level 0 to 1b Processing IODD.
The format description is also available on the web-page of the Basic Envisat Atmospheric Toolbox (BEAT), developed by S&T and available here. The BEAT Software provides a set of tools for ingesting, processing, and analyzing SCIAMACHY products.
6.2.7 Product Quality Information
A Readme file describing data quality and known instrument and processing issues as well as major improvements with respect to previous IPF versions is regularly maintained by the SCIAMACHY Quality Working Group and provided to the users. The document applying to the SCIAMACHY Level 1b products (SCI_NL__1P) is available here.
6.3 Operational Level 2 Products and Algorithms
The goal of the level 1b-2 data processing is to provide geophysical parameters as column densities, profiles from atmospheric constituents and cloud and aerosol parameters. Those data are given in the MDS of the level 2 product in combination with geolocation and additional auxiliary information (state geolocation, quality flagging, etc.) in the appropriate ADSs.
As outlined above, the operational level 1b-2 data processing occurs in Offline (OL) mode using two different types of processors, SCIAMACHY Ground Processor (SGP) L12 NRT and SGP L12 OL until 2006. In 2010 the fast delivery chain has been activated, using the same OL L2 processor, but NRT level 1 inputs. The level 1b-2 OL product includes retrievals from limb and nadir observation geometry. Algorithms and processors permanently evolve such that the product suite will be subject to changes. (see table 6-1)