Figure 1: SABER Level 1B dataflow

Download Level 1B Software Design Document in pdf format

• Scope
• Referenced Documents
• System Overview
• System Requirements
• Computer Software Configuration Items
• Open & Read Level 1A Files
• Identify Adaptive Scan Event & Required Data
• Space Look Processing
• IFC Processing
• Adaptive Scan Processing
• Acronym List
• Appendix A:  SABER Level 1B File Format Description

1. Scope

This Software Design Document (SDD) describes an overall design plan for SABER Level 1B processing software. The software reads in Level 1A data, performs signal processing and correction, converts the signals from volts to radiance units, and removes instrument and spacecraft motion effects. The data are then geolocated and gridded to common angle & height scales and output as a daily NetCDF file (see Appendix A).

2. Referenced Documents

• General Instrument Interface Specification [pdf]
• Level 1A Software Development Document: GATS-SABER-L1ASDD-98-1.V1 [pdf]

3. System Overview

The SABER Level 1B data flow is shown in Figure 1. The Level 1A file is ASCII format and is described in the Level 1A Format Document. It contains data merged into scan events, determined by the scan mode of the instrument.

4. System Requirements

The Level 1B software must be able to run on Linux workstations. It must be able to read and write files across the Internet via NFS.

5. Computer Software Configuration Items

5-1. Open & Read Level 1A Files

This CSCI opens and reads data from the SABER Level 1A file. The data are read into event classes, utilizing software from Level 1A processing with additional methods for reading.

Requirements

The CSCI must open a Level 1A file, determine the scan event mode from the scan mode flag in the event header, and load the data into specific classes depending on event type. Classes defined in Level1A processing will be reused by adding methods for reading in scan event data. Quality flags from Level 1A processing are tracked and passed with the data.

Testing

Each scan event class will have a method to dump data read in for comparison with Level 1A file.

5-2. CSCI:  Identify Adaptive Scan Event & Required Data

This CSCI searches through the adaptive scan class, finds the next adaptive scan event, and identifies the nearest bracketing Space Look and IFC events.

Requirements

The CSCI must read through the adaptive scan classes and find the next down and up pair of scans. The nearest space look and IFC events that bracket these data are then loaded for calibration processing.

Testing

Test data will be generated using data taken during calibration that places the instrument in all scan modes. These data will be run through Level 1A processing to generate a Level 1A file. This ASCII file will then be examined to determine the each adaptive scan event and correct bracketing Space Look and IFC events are identified for each Adaptive Scan Event.

5-3. CSCI:  Space Look Processing

This CSCI processes data taken by SABER when the mirror is staring at cold space to get a zero offset value for each channel.

Requirements

The CSCI must calculate the mean voltage for each channel for the duration of the Space Look events that bracket the current adaptive scan profile.

Testing

Measurements from calibration will be used to simulate Space Look events. These data will be evaluated for mean voltages for each channel. The mean voltages will be compared to the CSCI calculation.

5-4. CSCI:  IFC Processing

This CSCI processes data from looks at the In-Flight Calibrator in order to get coefficients for converting volts to radiance units for each channel. The known radiance S(T) is measured on the ground by transferring Blackbody calibration measurements. The on-orbit calibration coefficients are then computed by C = V/S(T), where T is known from IFC temperature measurements.

Requirements

The CSCI must read detector voltages and IFC temperatures for the duration of the IFC events that bracket the Adaptive Scan event. The IFC Source function (S(T(t)) where T(t) is the time-dependent IFC temperature) must be calculated using the calibration transfer measured on the ground. The calibration coefficient (C(t) = V(t)/S(T,t)) for each sample in time, must be computed and averaged over the time duration of the bracketing IFC events to give the calibration coefficient for each channel.

Testing

Simulated data from ground calibration will be used to generate IFC events in test Level 1A files. These data will be evaluated for mean calibration coefficients that will be compared to the coefficients calculated by the CSCI.

5-5. CSCI:  Adaptive Scan Processing

This CSCI processes (down-up) pairs of adaptive scans through the atmosphere.

Requirements

The CSCI must perform the following processing for each adaptive scan through the atmosphere:

-Deconvolve the electronic filter function from the data.

-Co-Align channels.

-Convert volts to radiance units.

-Estimate and remove any detectable spacecraft motion.

-Geolocate each sample and grid to uniform angle spacing.

-Write out each event profile in NetCDF format.

Testing

A simulated SABER Level 1A file will be generated from LIMS and SABER engineering calibration data. The test file will contain each scan mode identified in the SABER Level 1A SDD, as well as the simulated IFC and space-look events described in CSCI’s above. Specific tests for each requirement are described below:

Electronic Filter deconvolution: One adaptive scan event will have scans that consist of the Butterworth filter response to an input delta function. The module will successfully remove the electronics filter if a delta function is the output.

Co-Align Channels: Knife-edge data from engineering calibration will be used to validate the module’s ability to co-align each detector’s offset from the center of the focal plane.

Convert volts to radiance units: IFC data from engineering calibration will be used to validate the radiance output by the module based on the IFC and Jones Source Temperatures.

Estimate and remove any detectable spacecraft motion: Simulated PVAT data will be used which have attitudes perturbed which will cause known rotations to the simulated data. The module will be validated if it successfully removes these perturbations.

Geolocate each sample and grid to uniform angle spacing: Irregularly spaced data with known piece-wise linear values will be input to the gridding routines. The output data will have values that can be checked by verification.

Write out each event profile in NetCDF format: NetCDF reader software (i.e. IDL, Xmgr) will be used to validate the output NetCDF file.

6. Acronym List