Minimize SCIAMACHY Product Handbook

Short-Term Concept

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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.

6.2.4.1 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:


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The application of m-factors can be switched on and off by the Level 1 data users.

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M-factors are decoupled from the operational 0-1b processing; therefore a fast implementation is possible.

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Updates of the m-factor data base are possible independent from a Level 1 re-processing.


Only the m-factors describing the degradation of the science channels are needed here; the PMD m-factors are set to 1.

6.2.4.2 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:


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ATBD L0-1c: Algorithm theoretical baseline description for Level 0-1c processing.

This document describes in detail all calibration algorithms that are used in the operational processing.

The same algorithms are used by the SciaL1c tool.

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IODD: Input/output data definition for Level 0 and 1b.

This document contains a description of the level 1b format.

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SciaL1c SUM: Software user manual of the SciaL1c tool.

This document explains all user options and also contains a description of the level 1b and the level 1c product format.

 

The documents are available at the DLR web page.


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)


Spectral Range  Nadir    Limb 
UV-VIS-NIR O3 (vertical column)  HCHO (slant column)  O3 (profile) 
  NO2 (vertical column)  cloud cover  NO2 (profile) 
  BrO (vertical column)   cloud optical thickness  BrO (profile) 
  SO2 (vertical column)   cloud top height   
  OClO (slant column)  AAI   
  H2O (vertical column)     
SWIR CO (vertical column)     


Table 6-1: Operational SCIAMACHY level 2 product. The SWIR products are strongly affected by the icing in channels 7 and 8, and operational processing within the PDS needs major revisions to cope with the icing.

 


The general processing chain for the level 1b-2 data processors is outlined in fig. 6-4 (nadir) and 6-5 (limb). It presents the functional flow, but does not display software implementation. The SGP L12 OL is implemented as a multi-processor Linux cluster system. Particularly experience gained from scientific product generation will be reflected in the operational chain stepwise. Assuming that scientific algorithms are usually more evolved than the operational ones due to development timescales determined by the rules for PDS processor s/w updates, it is a valid scientific requirement to re-generate operational level 2 products whenever significant algorithm knowhow can be transferred from the scientific to the operational environment. Even beyond the in-orbit mission lifetime, an ambitious atmospheric science project like SCIAMACHY asks for requires continuing retrieval algorithm research and reprocessing. In the following subsections a rough overview of the used retrieval algorithms is given. Details can be found in the ATBD. (fig. 6-4, fig. 6-5)

 

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fig. 6-4:

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Offline level 2 processing part 1: Nadir and reading/writing of products. Continued in figure 6-5.
 

 

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