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
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.
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.
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/DT
DT = Accumulation Time
For channels with a double-bounded pass-band, the flux is calculated by:
Flux = Counts/(DT*DE*G)
DE = 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.
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).
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 |