***Software Interface Specification (SIS) for the Lunar Prospector
Spectrometer Planetary Data System Files, Version V002.2***

***Los Alamos National Laboratory Report LAUR-99-2754***

***D. J. Lawrence^1^, S. Maurice^2^, and W. C. Feldman^1^***

***^1^Los Alamos National Laboratory, Los Alamos, NM, USA***

***^2^Observatoire Midi-Pyrénées, Toulouse, France***

This document describes the file formats and data processing used for
the version 2.2 submission of Lunar Prospector Gamma-Ray Spectrometer
(GRS), Neutron Spectrometer (NS) and Alpha Particle Spectrometer (APS)
data to the Planetary Data System (PDS). The complete Version 2
submission will be described in a future SIS document.

***1. Gamma-Ray Spectrometer (GRS) Calibration Data***

*1.1 Calibration Set up*

Four isotopic sources of gamma rays were used for the calibration. These
sources, their strengths on the day of calibration (6 Nov., 1996), their
distance to the center of the BGO crystal, and the rate of gamma-rays
incident on the crystal (area = A~d~) are given in Table I.

**Table I**

**Gamma-Ray Sources used for Calibration of the LPGRS on 11/6/96**

**Source Source Strength (S) Distance (d) Sa~d~/(4πd^2^)**

Co-60 3.695 x 10^5^ s^-1^ 100 cm 8.57 s^-1^

Cs-137 3.928 x 10^5^ s^-1^ 100 cm 9.11 s^-1^

Yt-88 1.30 x 10^4^ s^-1^ 50 cm 0.302 s^-1^

Na-22 2.875 x 10^5^ s^-1^ 100 cm 6.67 s^-1^

The calibrations using the Co-60 and Yt-88 sources were conducted with
the GRS symmetry axis oriented perpendicular to the source direction,
and those using Cs-137 and Na-22 were oriented at angles spanning -90^o^
to +90^o^ to the perpendicular at 15^o^ intervals.

*1.2 Calibration Data Files*

There are 32 data files in ASCII column format which contain the LP GRS
calibration data. The column format is as follows:

> column 1: channel number (0 -- 511)
>
> column 2: calibrated energy in MeV
>
> column 3: number of *accepted* counts normalized to counts per 32
> seconds
>
> column 4: number of *rejected* counts normalized to counts per 32
> seconds

Definitions of *accepted* and *rejected* are given in references \[1\]
and\[2\].

The file names have the following format: run#\_source\_##\_deg.dat,
where

run#: designating run number

source: signifies which radioactive source was used

##\_deg: \## gives the angle of the source location---this angle ranges
from -90° to +90°.

***2. Neutron Spectrometer (NS)***

The Version 2.2 NS data contains one primary data file:
*NS_high2_V001.cdf*. This NS data file contains counting rate data for
thermal and epithermal neutrons from Oct. 7, 1998 to Dec. 19, 1998. This
file is the completion of the high altitude NS data and contains data
from the post-flip portion of the mission. Descriptions of the NS data
format, processing, and mission phase are given in the previous Version
1 and Version 2 SIS documents (references \[3\] and\[4\]).

***3. Alpha Particle Spectrometer (APS)***

*3.1 APS Data Contents*

Since one purpose of the APS is to look for time variable lunar gas
release events, the APS data is sorted by time instead of averaging into
lunar latitude/longitude pixels. The number of records is therefore not
fixed, but is determined by the number of measured alpha particle
counts. Table 4 lists the contents of the APS data. A description of
each variable is given below.

The *sf* variable is an integer variable. *sf* give the face number that
was triggered by each alpha particle. Figure 1 shows a diagram of how
each APS face is orientated relative to the LP spacecraft.

**lat:** Spacecraft longitude to the nearest 32-seconds.

**lon:** Spacecraft height to the nearest 32-seconds.

**hgt:** Spacecraft height to the nearest 32-seconds.

  -------------- --------- ----------------- ------------------------------
  Variable       Type      Unit              Description

  sf             integer   \<none\>          APS face number having values
                                             from 1 to 5

  lat            float     degrees           Spacecraft latitude for
                                             nearest 32-seconds.

  lon            float     degrees           Spacecraft longitude for
                                             nearest 32-seconds.

  hgt            float     kilometers        Spacecraft height for nearest
                                             32-seconds.

  ERT            float     seconds since Jan Earth receive time for each
                           1, 1970           alpha particle count.

  ph             integer   channel           Pulse height value for each
                                             alpha particle count.

  phi            float     degrees           Look angle from the orbital
                                             plane for each alpha particle
                                             count.

  aps_acc        float     counts per        Number of accepted counts
                           32-seconds        between *ph* channels 1 -- 126

  aps_buffer     float     counts per        Number of counts in the event
                           32-seconds        mode buffer for faces 1 -- 5.

  APS_scalar     integer   counts per        APS counting rate for the
                           32-seconds        nearest 32-seconds.
  -------------- --------- ----------------- ------------------------------

*Table 4: Contents of the APS.cdf file.*

**ERT:** Earth receive time for to the nearest 0.5 second for each of
the alpha particle counts. *ERT* is measured in seconds since January 1,
1970.

**ph:** Pulse height value of each alpha particle count. The *ph*
variable is measured as a channel number having values from 0 to 127.
The channels cover an alpha particle energy range of roughly 4.5 -- 6.6
MeV.

**phi:** The *phi* variable gives the de-spinned phase angle of each
face for each alpha particle count. This angle is defined as the angle
between normal of each face and the orbital plane.

**aps_acc**: The *aps_acc* variable gives the number of counts,
regardless of face, that occur for *ph* values of 1 -- 126.

**aps_buffer**: The *aps_buffer* variable gives the number of counts
that are measured in the APS event buffer. Since the event buffer can
only measure up to 294 counts (see \[2\]), *aps_buffer* is never any
larger than 294.

**aps_scalar:** The *aps_scalar* variable gives the total number of APS
events in the nearest 32-second data frame.

*3.2 APS Data Processing*

The main processing carried out with the APS data is to correct for the
spacecraft spin using sunpulse and ephemeris data. The result is a time
series data set consisting of data for each alpha particle count. These
data include: the pulse height value for each count (*ph*), the face
where the count occurred (*sf*), and the direction the face was pointing
(*phi*) relative to the plane of the spacecraft orbit. Note, the top and
bottom faces (faces 2 and 5) do not have a changing *phi* angle. The
orientation of these faces change with respect to the Moon only as a
function of latitude. These faces are therefore given *phi* angles of +1
(top face 2) and --1 (bottom face 5). A description of the APS
instrument can be found in reference \[2\].

*3.3 APS Data Format*

The APS data are stored as one file per day. The naming convention for
each file is as follows:

aps_YY_DOY~start~\_HHMM~start~\_DOY~end~\_HHMM~end~.cdf

where

YY = two digit year designation (i.e. 1998 = 98)

DOY~start~ = three digit day of year for the start time of the file

HHMM~start~ = four digit hours/minutes for the start time of the file

DOY~end~ = three digit day of year for the end time of the file

HHMM~end~ = four digit hours/minutes for the end time of the file.

The APS data is currently stored in Common Data Format (CDF). This
format has been described in a previous SIS \[1\]. A listing of the file
contents is given *aps-info.txt*. While the files have different
lengths, each file contains the same variables. CDF data files can be
read from a variety of platforms using a variety of software languages.
The Interactive Data Language (IDL) procedure called *load_cdf.pro*
(written by the LP spectrometer team and submitted to the PDS) can read
the APS data files inside the IDL environment. For example, to read the
*ph* and *phi* CDF variables into the PH and PHI IDL variables from the
file *aps_98_180_0000_98_181_0000.cdf*, do the following commands:

IDL\> load_cdf,'aps_98_180_0000_98_181_0000.cdf','ph',PH

IDL\> load_cdf,'aps_98_180_0000_98_181_0000.cdf','phi',PHI

***4. Summary of Data Files***

The following files make up the Version V002.2 LP spectrometer data
submission:

[Data files:]{.underline}

1.  Gamma-ray calibration data run##\_source_angle.dat

2.  Thermal and epithermal neutron data NS_high2_V002.cdf

3.  Alpha particle data
    aps_YY_DOY~start~\_HHMM~start~\_DOY~end~\_HHMM~end~.cdf

    [Content of data files:]{.underline}

## Neutron data NS_high2_V002-info.txt

## Alpha particle data APS-info.txt

***5. References***

\[1\] W. C. Feldman, B. L. Barraclough, K. R. Fuller, D. J. Lawrence, S.
Maurice, M. C. Miller, T. H. Prettyman, and A. B. Binder, The Lunar
Prospector Gamma-Ray and Neutron Spectrometers, *Nuclear Instruments and
Methods in Physics Research A*, 422, 562 -- 566, 1999.

\[2\] W. C. Feldman, D. J. Lawrence, S. Maurice, B. L. Barraclough, K.
R. Fuller, R. Belian, Lunar Prospector Spectrometers Instrument
Description Document, Los Alamos National Laboratory Report,
LAUR-99-2752, 1999.

\[3\] D. J. Lawrence, S. Maurice, and W. C. Feldman, Software Interface
Specification (SIS) for the Lunar Prospector Spectrometer Planetary Data
System Files, Version V001, Los Alamos National Laboratory Report
LAUR-99-2753, 1999.

\[4\] D. J. Lawrence, S. Maurice, and W. C. Feldman, Software Interface
Specification (SIS) for the Lunar Prospector Spectrometer Planetary Data
System Files, Version V002, Los Alamos National Laboratory Report
LAUR-99-2754, 1999.