MESSENGER EPPS EPS
EDR-to-CDR Processing
Version 1D
December 9, 2015
Prepared by
Lawrence Brown and Lillian Nguyen
The Johns Hopkins University
Applied Physics Laboratory
Table of Contents
1 PURPOSE 3
2 INTRODUCTION 3
3 CALIBRATION IMPLEMENTATION 3
4 CALIBRATION PROCEDURE 4
[NOTE: This is a plain text only version of the document. See the *.DOC or
*.PDF versions of this document for readable renderings of equations.]
1
Purpose
This document provides a description of the conversion of MESSENGER Energetic
Particle and Plasma Spectrometer (EPS) Experimental Data Records (EDRs) to
Calibrated Data Records (CDRs). The processing steps described in this
document represent the state of knowledge at the date of this document.
2 Introduction
The Science EDRs are the raw data records used to derive data used for
scientific analysis. The processing steps from the EDR to the CDR level are
described in this document.
3 Calibration Implementation
See the EPPS CDR SIS for a detailed description of instrument design issues
relevant to calibration. We present below the specific calibration algorithm
used in the production of EPS CDRs, including the Geometry/Efficiency factors
used. Note that by reporting "differential" flux, we are implicitly
"pretending" that the flux is constant across the energy band.
In practice, the CDR files are generated using the same Mission Independent
Data Layer (MIDL) codebase which also underlies the EPS Instrument Team's
science analysis software. The rates are read in from the EDR files as number
of counts in an accumulation interval. The rates in the CDR are then just
derived by the simple formula:
Rate = Counts/?T
?T = Accumulation Time
For channels with a double-bounded pass-band, the flux is calculated by:
Flux = Counts/(?T*?E*G)
?E = Upper Energy Bound - Lower Energy Bound
G = Geometry Factor = 0.0007 cm2-sr (large pixel)
0.000035 cm2-sr (small pixel)
Whether the instrument is operating in large or small pixel mode is determined
by the following: Before 2007:249 - small pixel mode except for
2005:214:13:16:1 -2005:214:15:42:59. After 2007:249 pixel mode is read from
the EPS_ION_PIX_SIZE or EPS_ELEC_PIX_SIZE field in the Long Status EDR.
4 Calibration Procedure
What follows is a summary of the procedure for applying the algorithm from the
previous section to produce CDR rates from EDR rates.
DT = Integration time (column 2 in the EDR)
C = The "Rate" value from the EDR. This is in raw counts accumulated over DT.
U = Upper energy bound in KeV. Get this from the table in the CDR SIS for the
Rate you're calibrating.
L = Lower energy bound in KeV. Also from the CDR SIS table.
G = Geometry factor (assumed energy independent for now). See previous
section for how to find.
Flux (in Counts/keV-cm2-sr-sec) = C/(DT*(U-L)*G).
5 Revision History
Rev
Date
Author(s)
Description
Sections
1A
15Jul2009
Lillian Nguyen Lawrence Brown
Initial version.
All
1B
03Dec2009
Lillian Nguyen Lawrence Brown
Overhaul after initial PDS review. Add section on calibration procedure.
4
1C
14Jan2010
Lillian Nguyen Lawrence Brown
Added revision history and fixed versioning.
5, title page
1D
09Dec2015
Susan Ensor
Final edits reflecting end of mission
All
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