Retrieval File Structure

Some users might be able to perform their own radiative transfer calculations and have access to a huge data set of radiosondes. A sophisticated design tool for the generation of system conform retrieval files is implemented in the “Files + Integration” tab sheet of the measurement definition window. The Define Retrieval File-button activates the retrieval design window.
Retrieval file names:
All retrieval files have the extension “.RET” to distinguish them from other file types. The first three characters of the file name indicate the retrieval product. For version 1.1 six products are implemented: TPT (temperature profile, troposphere), HPT (humidity profile, troposphere), LWP, IWV, ATN (Atmospheric Attenuation) and TPB (temperature profile, boundary layer). The next section (sections are separated from each other by the “_” character) of the file name is reserved for the retrieval type. Possible retrieval types are: LR (linear regression), QR (quadratic regression) and NN (neural networks). The third section contains the customer code and the forth section represents the version number. The file name sections are summarized in the editor’s “Category”-frame. The data base identifier is not used for the file name but is stored into the retrieval file for future purposes.
Retrieval File Structure :
With the “Load Retrieval File”-button load a “TPT_QR_CC_V1.RET”-file from the “…\2CH\RETRIEVALS\TPROFILE_TROP\”-directory (CC stands for the customer code). Retrieval files are text files which can be edited by any editor that does not insert any control codes or other characters that do not belong to the text. The content of the loaded retrieval file is displayed in the blue editor window.
The file starts with an identification code (6795005) utilized by R2CH to detect non-conformities caused by future changes in the file format. Comments are preceded by the “#”-character. All other text lines contain relevant data needed for the retrieval computation routines (2CH).
The continue character “:”at the beginning of a line indicates that this line belongs to the same parameter as the previous line. The continue code is used in the definition of matrices to add rows to a matrix.
A parameter code of 2 characters followed by a “=” character (no spaces!) specifies the meaning of the data that follows the “=” sign. The codes for the retrieval category are:

•	‘RP=’: Retrieval product. 0: LWP, 1: IWV, 2: Attenuation, 3: temperature profile (troposphere), 4: temperature profile (boundary layer), 6: humidity profile (troposphere) (mandatory parameter).
•	‘RT=’: Retrieval type. 0: linear regression, 1: quadratic regression, 2: neural network (mandatory).
•	‘CC=’: Customer code (mandatory parameter).
•	‘DB=’: Data Base
•	‘VN=’: Version number (mandatory parameter).

These codes must precede all other codes (except for the retrieval basis ‘RB=’).

Some retrievals include the surface sensor data as input parameters beside the brightness temperature data. In the “Included Sensors”-frame the retrieval designer checks the sensors he is going to include in his retrieval. The associated codes are:

•	‘TS=’: Temperature sensor. 0: sensor not used for retrieval, 1: sensor used (mandatory parameter).
•	‘PS=’: Pressure sensor. 0: sensor not used for retrieval, 1: sensor used (mandatory parameter).
•	‘HS=’: Humidity sensor. 0: sensor not used for retrieval, 1: sensor used (mandatory parameter).
•	‘IS=’: Infrared radiometer. 0: sensor not used for retrieval, 1: sensor used (mandatory parameter).

A neural network retrieval parameter is the number of intermediate knots (hidden knot layer). The associated parameter is:

•	‘NK=’: Number of intermediate knots (Neural Network only)

The presence of these codes in the retrieval file is mandatory.
Some retrieval designers prefer the optical thicknesses as input parameter instead of brightness temperatures. The code is:

•	‘RB=’: Retrieval basis. 0: brightness temperatures, 1: optical thicknesses (mandatory parameter).

All retrievals are based on microwave frequency channels. The frequency list must be preceded by:

•	‘FR=’: Frequency list [GHz] (mandatory parameter).

All observations are performed at certain elevation angles:

•	‘AG=’: Elevation angle list (mandatory parameter).

Those retrievals that produce data at certain altitudes (humidity and temperature profiles) must have an altitude parameter specified:

‘AL=’: Altitude list [m]

All other parameters are specific for the retrieval type.

Retrieval File Templates:
The user does not have to enter all these parameters by hand but instead defines his retrieval input and output parameters by filling the list boxes and check boxes in the retrieval editor. In addition, five comment lines may be entered for customer related information etc. By clicking on the “Generate Template”-button the editor text window is initialized with a syntactically correct retrieval file comprising all settings and numerical data is filled with zeros. 
The user must generate a text file which contains the retrieval coefficients in the same row and column order as required for the template. Then this coefficient file can be loaded with the “Load Data Matrix”-button and a second editor text window is opened containing this file. The user then copies and pastes the matrices from his coefficient file editor into the retrieval file editor text window. This concept ensures that the retrieval file syntax remains correct.