ROLO information for instrument teams Active

Information for Instrument Teams



The normal sequence of interaction between a Spacecraft Calibration Team (SCT) and the USGS Lunar Calibration Team (LCT) is:

1. Initial discussion between SCT and LCT about the suitability of lunar calibration for a specific instrument.

2. SCT provides the detailed spectral response for each instrument band.

3. LCT processes the spectral response data, and replies with the effective wavelengths for each band for white, solar, and lunar targets.

4. SCT becomes familiar with the data exchange items and file formats necessary to process their instrument Moon observations for lunar calibration (see Exchange File Formats).

For each lunar observation:

5. SCT processes their instrument lunar observation data and computes the necessary items of information, including the apparent (oversampled) lunar irradiance, calibrated to radiometric units.

6. SCT prepares the information exchange files for their lunar observations in the standard formats, and provides these to the LCT.

7. LCT computes the detailed geometry for each observation, queries the lunar irradiance model, and replies to the SCT with the geometry and irradiance comparison data.

These steps pertain exclusively to the use of disk-integrated lunar irradiance; procedures for comparison of spatially resolved lunar radiance will be available once a reliable radiance model is operational.

A major objective of the USGS lunar calibration program is to compare the radiance scales that are being used by the various spacecraft instruments. To facilitate this objective, SCTs are asked to provide their irradiance observations for comparison to the lunar irradiance model calculations. Lunar calibration results are communicated only to the SCT unless release is explicitly granted by the SCT.

Information Exchange Items

The two lists below define the interface between a Spacecraft Calibration Team (SCT) and the USGS Lunar Calibration Team (LCT) for model comparison of lunar irradiance observations. The interface is intentionally bilateral, i.e. the information will be available to both teams. There are standard Exchange File Formats for all items.

The SCT will provide to the LCT:

1. The system relative spectral response of each band. This is required only once unless the instrument is known to change.

2. The Universal Time (UTC) of the lunar observation. For scanning sensors, this is the time that the geometric center of the Moon is scanned, regardless of illumination. E.g. for push-broom systems, this is the time when the detector line array crosses the center of the Moon.

3. The location of the spacecraft at the above observation time, in (Earth-centered, inertial) J2000 Cartesian coordinates.

4. The oversampling of the Moon, or alternatively the apparent angular size of the Moon in the downtrack direction, in milliradians (Moon_Y_Size).

5. The apparent lunar irradiance measured in each band, without correction for distances or oversampling. Preferred units are microWatt m-2 nm-2. If the Moon is clipped, this is for the portion of the Moon observed. In order to track calibration histories, an identification of the radiometric calibration version used and the presumed pixel solid angle should be provided.

6. If the observed Moon is clipped, then the following two parameters are required for each focal plane. This assumes that the edge of coverage is a straight line across the lunar disk (a chord):

      1. The width of unobserved segment, as the angular distance from the center of the chord radially out to the lunar circumference expressed as a fraction of the lunar angular radius.

      2. The position angle of a line from the center of the Moon to the center of this chord, measured counterclockwise from equatorial celestial north.

The LCT provides to the SCT:

1. The spectral response data for each band, converted to an effective wavelength for a nominal lunar reflectance.

2. High precision geometry parameters pertaining to the locations of the Moon and Sun at the observation time, and all appropriate geometric correction factors.

3. Computation of the lunar irradiance model for the time and geometry of the spacecraft observation, interpolated the effective wavelengths of the spacecraft instrument bands. This includes correction for oversampling based upon the Moon_Y_Size parameter. Interpolations to spacecraft band wavelengths between the ROLO observational bands are done along a representative lunar reflectance curve. Panchromatic bands utilize a weighted sum of ROLO bands.

4. The discrepancy between the spacecraft measurement and the modeled lunar irradiance, expressed as a percentage: ((measured/model)-1.)*100%. This will include an identification of the lunar model version used.

5. If spacecraft image was clipped, an appropriate fractional correction to predict the irradiance from the entire Moon. (Prior to availability of a reliable lunar radiance model, this will be a simple geometric factor)

SCT Irradiance Processing

Spacecraft teams should produce an irradiance by doing a full radiance calibration of a lunar image using their usual or "best" calibration coefficients, presumably those used to produce their standard radiance data products. However, commonly a better zero-level radiance can be found from a lunar image (the surrounding space level) than from the standard data product processing. The irradiance is found by summing all the radiance pixels attributed to the Moon and multiplying by the nominal solid angle of a pixel (solid angle defined by sampling separation, not the MTF size of a pixel).

Note: this process is described in: H.H. Kieffer, P. Jarecke and J. Pearlman, "Initial Lunar Calibration Observations by the EO-1 Hyperion Imaging Spectrometer", Proc. SPIE 4480, 247-258, (2002); however, the SCT should not do any of the oversampling or distance corrections described therein.

If the oversampling of the Moon in an observation is not known, then the SCT must determine the apparent length of the Moon in their image, in milliradians. This must be done as accurately as possible, as the value enters linearly into the irradiance calculation. This is the limb-to-limb extent in pixels, multiplied by the down-track angular line spacing for normal nadir imaging.

Exchange File Formats

Currently all information exchange between a Spacecraft Calibration Team (SCT) and the USGS Lunar Calibration Team (LCT) is done with ASCII text files. The amount of information to be exchanged is modest, and ASCII files are easily read by both humans and computers. Eventually, comparisons of the spatially resolved lunar radiance will likely require binary information exchange.

Spectral Response Files (required only once)

The SCT should provide the system-level relative spectral response for each band, with a spectral resolution on the order of 1 nm (for spectrometers, the nominal full-width at half-maximum will generally be adequate). Absolute scaling is not important; the response functions can be normalized. A useful format for the LCT is a two-column ASCII text file for each band, with the first column being wavelength in nm and the second column being transmission or response. For response, the LCT must know whether the detectors respond to photons or energy.

Note: Once a band order is established for an instrument, that order should be maintained for all future file exchanges. Model results can optionally be sorted into ascending wavelength order.

Lunar Observation Files

The exchange files are generated by the SCT and LCT in pairs that roughly parallel one another. There are different formats for single and multiple observations of the Moon, with the Multiple Observation Files more common (time series of lunar views are the most useful; multiple observations are strongly encouraged). Because these files are ASCII text for input to computer programs, adherence to the standard formats is essential.

Each file begins with a label section that contains "keyword=value" entries, terminated by a separate line containing C_END. This section is followed by a table section containing the observation parameters (SCT) or model results (LCT). The label section may contain subsections, marked by the special keyword SECTION. This is done for readability, to distinguish the observational data supplied by the SCT from the model results generated by the LCT.

A line in the label section has the following elements:

• A keyword, with no interior blanks. Valid keywords are listed and defined below. Keywords must appear exactly as in the list (case-sensitive).

• An equal sign = between the keyword and value, with any number of blanks on either side (or none).

• A value, which may be numeric or alpha-numeric. Embedded blanks are allowed, as are any number of surrounding blanks. Units may be indicated, enclosed between < and > -- this is for readability only, units for each item are prescribed.

• An optional description/comment, initiated by an exclamation mark !.

• The special keyword BEGIN_FREE, which starts a free-form area within the label section. This area typically is used to describe the table section, with column headers, formats, etc. This area may contain any number of text lines, and is terminated by the C_END line. For readability, free-form text lines that extend beyond 80 columns are discouraged.

• The C_END line, which is always the last line before the table section.

The table section begins immediately after the C_END line, therefore any explicit column headers must appear before this line. The items in the table section must be space (not tab) delimited. Alignment is encouraged for human readability, but is not strictly required.

The contents of the label and table sections differ for single-observation and multi-observation files. For single observation files, the label section contains the observation geometry information, while the table section lists the irradiance information for each instrument band. For multiple observations, two sets of files are used, one (SCT/LCT pair) for geometry, one for irradiance. The rows of the table sections correspond to individual lunar observations, with the instrument bands arranged in columns. To accommodate all bands in one row, the table sections of these files can exceed an 80-character width. Further explanations of the table section contents have been appended in the examples below:

Example SCT Single Observation File

Instrument = EO-1 ALI

User = Jeff Mendenhall

Source_Date = ! Run Date/Time of primary input file

Image_Time = 2001-11-01T21:05:43.

Spacecraft_X = 5888.7 ! <km>

Spacecraft_Y = 1731.5 ! <km>

Spacecraft_Z = -3543.1 ! <km>

Moon_Y_size = 75.80 ! <mrad> Moon apparent diameter

Missing_Fraction = 0.0000 ! Areal fraction of Moon not observed

BEGIN_FREE ! Begins a free-form section describing the table section

This is a ROLO exchange file for: SCT Single-Observation

Col_0=index col_1=band col_2=nom. wavelength <nm>

Col_3=Instrument Irradiance <microW m^-2 nm^-1>

C_END

1 1p 442. 26.36

2 1 485. 30.67

3 2 567. 32.75

4 3 660. 30.63

5 4 790. 26.03

6 4p 865. 21.71

7 5p 1245. 13.63

8 5 1640. 7.39

9 7 2225. 3.01

10 10Pan 592. 28.47

The label section contains the geometry parameters for the observation. For

keyword definitions, see <Exchange File Formats>.

The contents of the table section are:

* column 1: A unity-based index of instrument bands

* column 2: The instrument-specific band identifier, numeric or alpha-numeric

* column 3: The nominal band center wavelength, expressed in nm

* column 4: The apparent lunar irradiance, in units of microWatts meter^-2 nanometer^-1

Additional columns (such as uncertainty) can easily be included in the tables.

Example LCT Single Observation File

SECTION = Observation info ! ----------------------- Begin a section

Instrument = EO-1 ALI ! Instrument makeing the observation

User = Jeff Mendenhall ! Person submitting the calibration request

Source_Date = ! Run Date/Time of primary input file

Image_Time = 2001-11-01T21:05:43. ! UTC at the middle of the observation

S_file_Name = 1 ! Name or lable of file received from Spacecraft team

Spacecraft_X = 5888.700 ! <km> Spacecraft X position at image-time in J2000

Spacecraft_Y = 1731.500 ! <km> Spacecraft Y position at image-time in J2000

Spacecraft_Z = -3543.100 ! <km> Spacecraft Z position at image-time in J2000

Moon_Y_size = 75.8000 ! <mrad> Moon apparent diameter along slew

Missing_Fraction = 0.0000 ! Areal fraction of Moon not observed

Clip_Angle = 0.000 ! <degree> Position Angle of missing section, ccw from N

SECTION = ROLO_Calculations ! ----------------------- Begin a section

Process = iradcal ! Name of process that generated this file

Version = 2005jul23 ! Processing version

Run_Time = 2006Feb14 12:58:00 ! Local Date/Time of these calculations

Lunar_model = 311g = [coeff=r311g adjust=r311g05 ] ! Identification of the Lunar irradiance model used

Barycentric_Time = 2452215.3797127609 ! <day> Dynamical barycentric Julian date

Sun_Moon_lon = -11.935 ! <degree> Selenographic longitude of the Sun

Sun_Moon_lat = 1.224 ! <degree> Selenographic latitude of the Sun

SC_Moon_lon = -3.748 ! <degree> Selenographic longitude of spacecraft

SC_Moon_lat = 3.880 ! <degree> Selenographic latitude of spacecraft

SC_Distance = 386394.7 ! <km> Distance of spacecraft from center of Moon

Sun_Moon_Distance = 0.9948765 ! <AU> Heliocentric range of the Moon

Distance_Factor = 1.000078 ! Factor to correct irradiance to standard distances

Phase_angle = 8.599 ! <degree> Signed phase angle

Moon_Diam_Angle = 8.9929 ! <mrad> Diameter of the Moon from SC

Axis_Angle = -14.916 ! <degree> Position Angle of lunar axis, ccw from N

Oversample_Factor = 8.429 ! Image oversample factor

Flux_Factor = 0.118640 ! Factor for Units, Oversample and missing fraction

NOTE =

NOTE = Col_0=index col_1=band col_2=nom. wavelength <nm>

NOTE = Col_3=Instrument Irradiance <microW m^-2 nm^-1> Col_4=effective wavelength

NOTE = Col_5=model Irradiance col_6=% disagreement col_7=Instrument: scaled

C_END

0 1p 442.00 26.3600 442.25 2.8969 7.96 3.1273

1 1 485.00 30.6700 485.70 3.3652 8.13 3.6387

2 2 567.00 32.7500 568.29 3.5884 8.28 3.8854

3 Pan 592.00 28.4700 596.45 3.5199 -4.04 3.3777

4 3 660.00 30.6300 660.17 3.4093 6.59 3.6339

5 4 790.00 26.0300 789.97 2.8405 8.72 3.0882

6 4p 865.00 21.7100 865.61 2.4398 5.57 2.5757

7 5p 1245.00 13.6300 1244.20 1.5005 7.77 1.6171

8 5 1640.00 7.3900 1637.83 0.9123 -3.90 0.8767

9 7 2225.00 3.0100 2218.78 0.3390 5.35 0.3571

The label section is supplemented with ephemeris and geometric correction

parameters computed by the LCT. For keyword definitions, see <Exchange

File Formats>.

The contents of the table section are:

* column 1: A zero-based index of instrument bands

* column 2: The instrument-specific band identifier, in wavelength order

* column 3: The nominal band center wavelength in nanometers

* column 4: The apparent instrument lunar irradiance, in microWatts meter^-2 nanometer^-1

* column 5: The effective wavelength of the band for a lunar spectrum, in nanometers

* column 6: The lunar model irradiance for the observation conditions, in microWatts meter^-2 nanometer^-1

* column 7: The percent disagreement between the spacecraft and lunar model, as ((spacecraft/model)-1.)*100%

* column 8: The spacecraft irradiance for the complete Moon, after applying the Flux_Factor

Example SCT Geometry Multiple Observation File

SECTION = Observation info ! ----------------------- Begin a section

Instrument = EO-1 ALI ! Instrument makeing the observation

User = Jeff Mendenhall ! Person submitting the calibration request

Source_Date = ! Run Date/Time of primary input file

Process = MIT/LL IDL ! Name of process that generated this file

Version = 2002sept10 ! Processing version

Run_Time = 2003 Dec 04 ! Local Date/Time of these calculations

BEGIN_FREE ! Begins a free-form section describing the table section

This is a ROLO exchange for: SCT MOS geometry

Col_0=Obs_index col_1=Image_time col_2,3,4=Spacecraft_X,Y,Z

Col_6=Moon_Y_Size [ Col_7=Miss_Frac Col_8=Clip_angle ]

Format = (i3,1x,a21,3f9.1,f10.3,f7.4,f7.1)

C_END End of label section

1 2001-02-07T19:45:11. -2379.9 4967.5 -4460.5 80.67 0.0000 0.0

2 2001-03-10T04:10:11. -4183.0 2697.5 -5046.4 80.14 0.0000 0.0

3 2001-04-07T17:44:44. -4776.8 339.5 -5225.6 81.57 0.0000 0.0

4 2001-05-08T02:06:43. -2508.3 -1717.5 -6403.8 80.18 0.0000 0.0

5 2001-06-05T10:42:11. -266.7 -1656.5 -6887.8 76.99 0.0000 0.0

6 2001-07-06T06:43:44. 185.4 -2893.7 -6469.0 70.89 0.0000 0.0

7 2001-08-04T21:02:44. 1580.3 -2500.0 -6442.0 72.28 0.0000 0.0

8 2001-09-02T07:20:44. 2687.4 -1620.7 -6356.0 70.64 0.0000 0.0

9 2001-10-03T01:46:44. 5186.7 -950.7 -4736.7 72.81 0.0000 0.0

10 2001-11-01T21:05:43. 5888.7 1731.5 -3543.1 75.80 0.0000 0.0

The label section contains information on the processing used to create this

file. For keyword definitions, see <Exchange File Formats>.

The table section contains a row for each lunar observation. The columns

are the observation geometry parameters, exactly analogous to the keywords

defined for a SCT Single Observation File.

* column 1: A unity-based index of instrument lunar observations

* column 2: Image_Time

* column 3: Spacecraft_X

* column 4: Spacecraft_Y

* column 5: Spacecraft_Z

* column 6: Moon_Y_size

* column 7: Missing_Fraction

* column 8: Clip_Angle

Example SCT Irradiance Multiple Observation File

SECTION = Observation info ! ----------------------- Begin a section

Instrument = EO-1 ALI ! Instrument makeing the observation

User = Jeff Mendenhall ! Person submitting the calibration request

Process = MIT/LL IDL ! Name of process that generated this file

Version = 2002sept10 ! Processing version

Run_Time = 2003 Dec 04 ! Local Date/Time of these calculations

BEGIN_FREE ! Begins a free-form section describing the table section

This is a ROLO exchange for: SCT MOS Irradiance

See matching Geometry file for comments

Col_0 = Obs_index Col_1+ = Irradiance in bands

Units are: microWatts / m^2 / nm

Format = (i3,12f9.4)

-1 1p 1 2 3 4 4p 5p 5 7 Pan

-2 442. 485. 567. 660. 790. 865. 1245. 1640. 2225. 592.

C_END End of label section

1 33.06 38.56 41.14 39.30 33.53 28.23 17.50 9.50 3.87 35.42

2 30.75 35.63 37.83 35.55 30.19 25.16 15.68 8.46 3.43 33.21

3 31.04 36.13 38.51 36.32 30.94 25.88 16.18 8.72 3.55 33.41

4 29.43 34.22 36.41 34.18 29.04 24.28 15.12 8.16 3.30 31.61

5 26.46 30.80 32.88 30.73 26.17 21.87 13.72 7.42 3.01 28.52

6 24.49 28.39 30.09 28.05 23.72 19.75 12.29 6.62 2.67 26.48

7 23.63 27.41 29.19 27.21 23.06 19.20 12.04 6.50 2.63 25.53

8 24.34 28.28 30.09 28.10 23.83 19.87 12.42 6.69 2.71 26.18

9 25.27 29.31 31.16 29.05 24.60 20.46 12.75 6.89 2.79 27.29

10 26.36 30.67 32.75 30.63 26.03 21.71 13.63 7.39 3.01 28.47

The label section contains information on the processing used to create this

file. For keyword definitions, see <Exchange File Formats>.

The table section contains a row for each lunar observation, which must be

aligned with the SCT Geometry Multiple Observation File. Instrument bands are

arranged in columns. The table section can exceed 80-character width.

* column 1: A unity-based index of instrument lunar observations

* columns 2-n: For each instrument band, the apparent lunar irradiance in microWatts meter^-2 nanometer^-1

Example LCT Geometry Multiple Observation File

SECTION = Observation info ! ----------------------- Begin a section

Instrument = EO-1 ALI ! Instrument makeing the observation

User = Jeff Mendenhall ! Person submitting the calibration request

Source_Date = 2003 Dec 04 ! Run Date/Time of primary input file

Process = iradcal & multimoon ! Name of process that generated this file

Version = 2005jul23 & 2005jul24 ! Processing version

Run_Time = 2006Feb14 13:57:12 ! Local Date/Time of these calculations

BEGIN_FREE ! Begins a free-form section describing the table section

This is a ROLO exchange for: LCT MOF geometry

GUIDE to columns below:

Col Key units Description

0 Row - Observation Count

1 TDB-2451545 day Dynamical barycentric Days -2451545.

2 SunLon degree Selenographic longitude of the Sun

3 SunLat degree Selenographic latitude of the Sun

4 SC_Lon degree Selenographic longitude of spacecraft

5 SC_Lat degree Selenographic latitude of spacecraft

6 SC_Dist. km Distance of spacecraft from center of Moon

7 Sun_M_Dist AU Heliocentric range of the Moon

8 DistFac - Factor to correct irradiance to standard distances

9 PhaseAng degree Signed phase angle

10 Moon_mrad mrad Angular Diameter of the Moon from SC

11 Axis_Ang degree Position Angle of lunar axis, ccw from N

Format = (I3,1x,f13.6,1x,f8.2,1x,f5.2,1x,f6.2,1x,f6.2,1x,f8.1,1x,F9.7,1x,f9.6,1x,F8.3,1x,f8.4,1x,f8.3)

Row TDB-2451545 SunLon SunLat SC_Lon SC_Lat SC_Dist. Sun_M_Dist DistFac PhaseAng Moon_mrad Axis_Ang

C_END End of label section

1 403.323792 6.40 -0.89 -0.44 -4.11 353512.4 0.9887706 0.826863 -7.561 9.8294 17.931

2 433.674469 -2.95 -1.42 3.27 -7.25 358957.7 0.9955547 0.864271 8.513 9.6802 23.970

3 462.240143 8.95 -1.52 3.48 -7.37 363747.8 1.0036108 0.901913 -7.995 9.5528 22.785

4 492.588745 -1.29 -1.19 5.08 -5.42 377681.8 1.0117936 0.988255 7.634 9.2003 12.921

5 520.946716 12.31 -0.57 4.80 -4.16 384838.9 1.0171890 1.037037 -8.318 9.0292 7.981

6 551.781128 -4.50 0.26 3.00 1.17 396448.7 1.0192988 1.105122 7.555 8.7648 -10.688

7 581.377625 -6.21 1.00 0.96 4.03 401291.3 1.0170912 1.127385 7.783 8.6590 -19.674

8 609.806824 6.53 1.47 0.30 5.02 401747.1 1.0115631 1.117698 -7.160 8.6492 -22.275

9 640.574890 -8.82 1.57 -2.63 5.84 395920.5 1.0032324 1.067708 7.505 8.7765 -22.098

10 670.379700 -11.94 1.22 -3.75 3.88 386394.7 0.9948765 1.000078 8.599 8.9929 -14.916

The label section propagates the processing information used to create the SCT

Multiple Observation Files, and adds explanations of the columns in the table

section, including FORTRAN-style format statements and aligned column headers.

The table section contains a row for each lunar observation, row-aligned with

the SCT Multiple Observation Files. The columns give the ephemeris and

geometric correction parameters computed by the LCT, analogous to the keywords

defined for a LCT Single Observation model results file. For keyword

definitions, see <Exchange File Formats>.

* column 1: A unity-based index of instrument lunar observations

* column 2: Barycentric_Time minus 2451545.0

* column 3: Sun_Moon_lon

* column 4: Sun_Moon_lat

* column 5: SC_Moon_lon

* column 6: SC_Moon_lat

* column 7: SC_Distance

* column 8: Sun_Moon_Distance

* column 9: Distance_Factor

* column 10: Phase_angle

* column 11: Moon_Diam_Angle

* column 12: Axis_Angle

Example LCT Irradiance Multiple Observation File

SECTION = Observation info ! ----------------------- Begin a section

Instrument = EO-1 ALI ! Instrument makeing the observation

User = Jeff Mendenhall ! Person submitting the calibration request

Process = iradcal & multimoon ! Name of process that generated this file

Version = 2005jul23 & 2005jul24 ! Processing version

Run_Time = 2006Feb14 13:57:12 ! Local Date/Time of these calculations

Lunar_model = 311g = [coeff=r311g adjust=r311g05 ]

!! Corrections:

BEGIN_FREE ! Begins a free-form section describing the table section

This is a ROLO exchange for: LCT MOF Irradiance

See matching Geometry file for comments

GUIDE to columns below:

Headers: Row-1=band

Row-2=Nominal wavelength

Row-3=Effective wavelength for the Moon

Table : Col_0=count Col_1=oversample factor. Remaining columns are

% disagreement, with a row for each observation

(Spacecraft_Irradiance/ROLO_Irradiance -1.) in percent.

Format = (i3,f8.4,12f8.2)

-1 1p 1 2 Pan 3 4 4p 5p 5 7

-2 442. 485. 567. 592. 660. 790. 865. 1245. 1640. 2225.

-3 442.25 485.70 568.29 596.45 660.17 789.97 865.61 1244.20 1637.83 2218.78

C_END End of label section

1 8.2070 7.97 8.47 8.63 -4.64 9.29 12.00 9.98 11.12 -0.56 9.30

2 8.2787 7.91 7.62 7.15 -4.12 5.94 7.96 4.82 6.25 -5.68 2.88

3 8.5389 7.26 7.48 7.46 -4.96 6.65 9.05 6.39 8.32 -3.83 5.42

4 8.7149 8.62 8.80 8.68 -3.79 7.47 9.71 6.91 8.48 -3.52 5.32

5 8.5267 6.65 6.84 6.93 -5.47 5.10 7.35 4.65 6.85 -4.84 3.78

6 8.0880 9.89 9.74 9.22 -1.97 7.29 9.04 5.79 7.27 -4.77 3.74

7 8.3473 6.35 6.26 6.23 -5.25 4.32 6.22 3.04 5.24 -6.40 2.20

8 8.1672 7.45 7.57 7.50 -4.61 5.79 7.83 4.88 6.92 -5.00 4.03

9 8.2960 7.78 7.71 7.55 -3.93 5.68 7.58 4.23 5.85 -5.73 3.16

10 8.4289 7.96 8.13 8.28 -4.04 6.59 8.72 5.57 7.77 -3.90 5.35

The label section propagates the processing information used to create the SCT

Multiple Observation Files, and adds explanations of the columns in the table

section, including FORTRAN-style format statements and aligned column headers.

The table section contains a row for each lunar observation, row-aligned with

the SCT Multiple Observation Files. The table gives the lunar model results

as comparisons, with the instrument bands arranged in columns. The table

section can exceed 80-character width.

* column 1: A unity-based index of instrument lunar observations

* column 2: The Oversample_Factor (see <Exchange File Formats>)

* columns 3-n: For each instrument band, the percent disagreement between the spacecraft and lunar model, as ((spacecraft/model)-1.)*100%

Label Section Keywords

The keywords appearing in an exchange file label section are specific to the file type. Keyword definitions for each file type are listed below. All keywords must appear in the label section of SCT files, in the order listed (except the optional keyword NOTE).

SCT Single Observation File Keywords

Instrument = A unique identification of the instrument, possibly including separate optical components, e.g. ASTER SWIR. Internal blanks are allowed.

User = The name of the (one) person representing the SCT. Internal blanks are allowed.

Image_Time = Coordinated Universal Time (UTC) of the observation. For a push-broom system, this should be the time when the scan line crossed the geometric center of the Moon. The format is specific, and consistent with ISO-8601 (See http://www.w3.org/TR/NOTE-datetime). It must follow exactly (as in the single observation example linked above, 2001-11-01T21:05:43.):

four decimal characters of year

a dash (-)

two decimal characters of month

a dash (-)

two decimal characters of day within month

a "T" (T)

two decimal characters of hour

a colon (:)

two decimal characters of minute

a colon (:)

two decimal characters of integral second

optionally followed by a decimal point and decimal fraction of a second.

Spacecraft_X = The X coordinate of the spacecraft position at Image_Time in the J2000 coordinate system, expressed in kilometers. This is the non-rotating coordinate system normally used for orbital dynamics calculations.

Spacecraft_Y = The corresponding Y coordinate.

Spacecraft_Z = The corresponding Z coordinate.

Moon_Y_size = The apparent diameter of the Moon in the direction of elongation (or compression) of the image due to scanning, expressed in milliradians. This is measured to the geometric limbs, one possibly unilluminated. If the oversampling of the observation is known accurately, then this keyword can contain the oversampling factor (the SCT must inform the LCT if the oversampling factor is being used). For a framing imaging system that completely captures the Moon with short exposure time, this value is not needed (keyword is set to zero).

The following two keywords are relevant only if the Moon was not completely captured in the image, hence in the irradiance sum.

Missing_Fraction = The areal fraction of the geometric Moon not represented in the irradiance sum.

Clip_Angle = The azimuthal angle measured counterclockwise about the geometric center of the Moon from Celestial North to the middle of the missing section, expressed in degrees.

NOTE = A free-form line containing any additional text.

LCT Single Observation File Keywords

The label section for a LCT Single Observation File contains two subsections, marked by SECTION = lines. The first repeats the SCT label information, as a check. The second contains the computed geometric parameters for the observation, in the following keywords.

Process = The name of the software system that ran the model comparison.

Version = The version date of the Process software that was used.

Run_Time = The local date and time of the model run, as YearMonthDay hour:minute:second

Lunar_model = Identification of the lunar model version used. This includes identification of the model coefficients files used.

Barycentric_Time = Image_Time converted to barycentric dynamical time, expressed as a double-precision Julian date. This is the continuous, uniform time system used for planetary ephemeris calculations, and differs somewhat from UTC.

Sun_Moon_lon = The Selenographic longitude of the sub-solar point on the Moon, in degrees.

Sun_Moon_lat = The Selenographic latitude of the sub-solar point on the Moon, in degrees.

SC_Moon_lon = The Selenographic longitude of the sub-spacecraft point on the Moon, in degrees.

SC_Moon_lat = The Selenographic latitude of the sub-spacecraft point on the Moon, in degrees.

SC_Distance = The distance of the spacecraft from the center of the Moon at Image_Time, in kilometers.

Sun_Moon_Distance = The distance from the center of the Sun to the center of the Moon at Image_Time, in Astronomical Units (AU).

Distance_Factor = The multiplying factor to convert measured irradiance to that expected with the same geometric angles but with the spacecraft and Sun at standard distances from the Moon (384,400 km and 1 AU, respectively).

Phase_angle = The Sun-Moon-Spacecraft angle, in degrees, negative before Full Moon.

Moon_Diam_Angle = The angular diameter of the Moon (assumed circular) viewed from the spacecraft at Image_Time, expressed in milliradians.

Axis_Angle = The apparent orientation of the Lunar North polar spin axis, measured counterclockwise from Celestial North, in degrees.

Oversample_Factor = The image oversample factor, i.e. the factor by which the simple irradiance sum of a spacecraft image over-represents the true irradiance.

Flux_Factor = A composite multiplication factor applied to the spacecraft apparent irradiance to account for oversampling, any missing fraction of the Moon, and any radiometric units conversion.

SCT Multiple Observation File Keywords

SCT geometry and irradiance Multiple Observation Files are typically generated by some sort of automated process from primary data files native to the SCT. The keywords for these files are intended to track their origin, and are used only to

propagate this information to the LCT files. The keywords for SCT Geometry and Irradiance Multiple Observation Files are identical.

Instrument = A unique identification of the instrument, possibly including separate optical components, e.g. ASTER SWIR. Internal blanks are allowed.

User = The name of the (one) person representing the SCT. Internal blanks are allowed.

Source_Date = The date and time of the primary SCT observational data file.

Process = the name of the software system that created this input file.

Version = The version date of the Process software that was used.

Run_Time = The data and time when this input file was created by Process. Internal blanks are allowed.

LCT Multiple Observation File Keywords

The Instrument and User keywords from the SCT Multiple Observation Files are propagated to the LCT geometry and model results Multiple Observation Files. The keywords Process and Version are modified to values for the software system that ran the model comparison. Run_Time is updated to the local date and time of the model run. One new keyword is added to the LCT model results file:

Lunar_model = Identification of the lunar model version used. This includes identification of the model coefficients files used.

The BEGIN_FREE sections generated for LCT Multiple Observation Files contain extensive explanations of the columns, including FORTRAN-style format statements and column-aligned headers.