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SST record 50 km cell MDS
BT/TOA Sea record 17 km cell MDS
ATS_TOA_1P_MDSR_conf
ATS_TOA_1P_MDSR_cl
ATS_TOA_1P_ADSR_pix
ATS_SST_AX_GADSR
Vegetation fraction for Land Surface Temperature Retrieval GADS
Topographic Variance data for Land Surface Temperature Retrieval GADS
Land Surface Temperature retrieval coefficients GADS
General Parameters for Land Surface Temperature Retrieval GADS
Climatology Variance Data for Land Surface Temperature Retrieval GADS
Level 0 SPH
Level 0 MDSR
Auxilliary Data SPH with N = 1
1.6 micron nadir view MDS
Summary Quality ADS
Scan pixel x and y ADS
Grid pixel latitude and longtitude topographic corrections ADS
Across-track Band Mapping Look-up Table
Configuration Data GADS
Processor configuration GADS
LST record 50 km cell MDS
Distributed product MDS
Level 2 SPH
SPH
10-arcminute mds
Limits GADS
Validation Parameters GADS
BT/TOA Land record 17 km cell MDS
General Parameters GADS
Temperature to Radiance LUT GADS
Radiance to Brightness Temperature LUT GADS
Medium/High Level Test LUT GADS
Infrared Histogram Test LUT GADS
11 Micron Spatial Coherence Test LUT GADS
11/3.7 Micron Nadir/Forward Test LUT GADS
11/12 Micron Nadir/Forward Test LUT GADS
Characterisation GADS
Browse Day_Time Colour LUT GADS
Browse SPH
Grid pixel latitude and longtitude topographic correction ADS
Level 2 SPH
Auxilliary Products
ATS_VC1_AX: Visible Calibration data
ATS_SST_AX: SST Retrieval Coeficients data
ATS_PC1_AX: Level-1B Processing configuration data
ATS_INS_AX: AATSR Instrument data
ATS_GC1_AX: General Calibration data
ATS_CH1_AX: Level-1B Characterization data
ATS_BRW_AX: Browse Product LUT data
Level 0 Products
ATS_NL__0P: AATSR Level 0 product
Browse Products
ATS_AST_BP: AATSR browse image
Level 1 Products
ATS_TOA_1P: AATSR Gridded brightness temperature and reflectance
Level 2 Products
ATS_NR__2P: AATSR geophysical product (full resolution)
ATS_MET_2P: AATSR Spatially Averaged Sea Surface Temperature for Meteo Users
ATS_AR__2P: AATSR averaged geophysical product
Frequently Asked Questions
The AATSR Instrument
Instrument Characteristics and Performance
In-flight performance verification
Instrument Description
Internal Data Flow
Instrument Functionality
AATSR Products and Algorithms
Common Auxiliary data sets
Auxiliary Data Sets for Level 2 processing
Instrument Specific Topics
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Level 1B Products
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The Level 0 Product
Differences Between ATSR-2 and AATSR Source Packets
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AATSR Product Organisation
Data Handling Cookbook
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Monitoring of AATSR VISCAL Parameters
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Introduction
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The AATSR Products User Guide
Image Gallery
Breakup of the Ross Ice Shelf
Land cover in the Middle East
Typhoon Saomai
Mutsu Bay, Japan
Deforestation in Brazil
Spatially Averaged Global SST, September 1993
Further Reading
How to use AATSR data
Why Choose AATSR Data?
Why Choose AATSR Data?
Special Features of AATSR
Principles of Measurement
Scientific Background
The AATSR Handbook
SST record 17 km cell MDS
Surface Vegetation class for Land Surface Temperature Retrieval GADS
1.6 micron forward view MDS
12 micron nadir view MDS
12 micron forward view MDS
Summary Quality ADS
Surveillance Limits GADS
Master Unpacking Definition Table GADS
1.6 micron Non-Linearity Correction LUT GADS
General Parameters GADS
Thin Cirrus Test LUT GADS
Fog/low Stratus Test LUT GADS
1.6 Micron Histogram
Browse MDS
ATS_CL1_AX: Cloud LUT data
Glossary
Pre-flight characteristics and expected performance
Payload description, position on the platform
Auxiliary products
Auxiliary Data Sets for Level 1B processing
Summary of auxiliary data sets
Calculate Solar Angles
Image Pixel Geolocation
Level 0 Products
Acquisition and On-Board Data Processing
Product Evolution History
Hints and Algorithms for Higher Level Processing
Data Volume
Software tools
Summary of Applications vs Products
Geophysical Coverage
Geophysical Measurements
ATS_TOA_1P_ADSR_sa
Visible calibration coefficients GADS
Level 1B SPH
LST record 17 km cell MDS
Conversion Parameters GADS
12 Micron Gross Cloud Test LUT GADS
ATS_PC2_AX: Level-2 Processor Configuration data
Level 2 Products
Hints and Algorithms for Data Use
BT/TOA Sea record 50 km cell MDS
BT/TOA Land record 50 km cell MDS
Level 2 Algorithms
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2.6.2 Level 1B Products

2.6.2.1 Structure of AATSR gridded products

Although the scanning geometry of AATSR is such that measured pixels lie on a sequence of curved instrument scans, AATSR image data is presented on a rectangular grid of points centered on the satellite ground track and of approximately 1 km resolution (but spaced by equal time intervals along-track).

To be precise, the sampling interval between grid points ('image pixels') is 1 km in the across-track (x) direction, but in the along track (y) direction it is equal to the distance moved by the sub-satellite point in one scan interval of 150 ms. This is approximately equal to 1 km, but varies around the orbit with the satellite velocity.

This sampling scheme differs from that used in ATSR and ATSR-2 processing by the introduction of equal time interval sampling. The move to equal time interval sampling was motivated in part by the change to orbit based products (ATSR and ATSR-2 products are based on 512 km square images). Equal time interval sampling permits (though it does not guarantee) continuity of sampling in the overlap region. It also permits the revised regridding scheme to operate with minimal impact on the cosmetic fill algorithm.

The standard AATSR image grid is 512 km wide, so that each row of the image contains 512 pixels. The AATSR image products at both Level 1B and Level 2 are structured so that each Measurement data record corresponds to one image row of 512 pixels.

2.6.2.1.1 ATS_TOA_1P

The Gridded Brightness Temperature/Reflectance (GBTR) product is the single Level 1B product from AATSR. It contains top of atmosphere (TOA) brightness temperature (BT) values for the three infra-red channels and reflectance values for the 1.6 µm and visible channels. Values for each channel and for the nadir and forward views occupy separate measurement data sets as shown in [Formats 6.2.1. ]. Additional MDS contain cloud and land/sea flags and confidence flags for each image pixel.

The product contains the following measurement data sets.

Table 2.16 Level 1B (GBTR) Product
MDS Channel/µm View Application
1 12.0 nadir Surface temperature, cloud clearing
2 11.0 nadir Surface temperature, cloud clearing
3 3.7 nadir Surface temperature, cloud clearing
4 1.6 nadir Cloud clearing
5 0.87 nadir Vegetation index
6 0.67 nadir Vegetation index
7 0.55 nadir Chlorophyll
8 12.0 forward Surface temperature, cloud clearing
9 11.0 forward Surface temperature, cloud clearing
10 3.7 forward Surface temperature, cloud clearing
11 1.6 forward Cloud clearing
12 0.87 forward Vegetation index
13 0.67 forward Vegetation index
14 0.55 forward Chlorophyll
15 all nadir Confidence words
16 all forward Confidence words
17 all nadir Cloud and land/sea flags
18 all forward Cloud and land/sea flags

Each measurement data set has a similar structure, in which four header fields precede 512 fields of image row data:

  • Nadir time field;
  • Record quality indicator;
  • Spare field; three spare bytes to ensure that subsequent data fields are aligned on a 4-byte boundary;
  • Image scan y co-ordinate.

The nadir time field contains the time tag assigned to the record. Because of the curved scan geometry of AATSR, the pixels making up a gridded record are measured at a wide range of times, and it is not possible to assign a single time that applies to the record as a whole. The time shown here is that which applies to the pixel at the centre of the scan (which is in fact the latest to be measured) and is calculated as the time at which the sub-satellite point coincided with the along-track pixel of the scan. The time tag assigned to a forward view record is the same as that of the corresponding nadir view record, hence the designation 'nadir time'. This ensures that coincident records have the same time field. (The forward view of a given region is measured some 2.5 minutes earlier than the nadir view because of the conical scan geometry.

The record quality indicator is a flag that is set to -1 if the record contains no valid data, and to 0 otherwise. This definition is generic, and applies to all ENVISAT instruments. In the particular case of AATSR, the curved scan geometry is such that each record may contain pixels from 100 or more instrument scans. In addition, pixels that represent an invalid measurement are set to an exception value that gives information about the precise reason that the datum is invalid. Exception values convey information, and (except for null pixels) are therefore considered to be valid data in the context of this flag. For both of these reasons it is therefore unlikely that a record will contain no valid data, and the record quality indicator will only be set in a substantial data gap.

Image scan y co-ordinate: Image pixels in the AATSR products are described by their co-ordinates in a quasi-Cartesian XY system, in which the Y axis is tangent to the satellite ground track at any point. The Image Scan Y co-ordinate is the along-track Y co-ordinate of all the pixels on the image row contained in the record. It is the along-track distance, in metres, of the image scan measured along the sub-satellite track from an origin which depends on the product. In the case of consolidated products the origin is the ascending node of the orbit on the equator, but in the case of NRT products the origin is an arbitrary point at the start of the product, measured in km.

The remainder of the record provides the pixel value or corresponding flags word, depending on the MDS. For those MDS that contain the measured pixel, data, the pixel value represents the brightness temperature in units of 0.01K for the thermal infra-red channels, or the calibrated reflectance in units of 0.01% for the 1.6 micron and visible channels. It is possible that a valid physical measurement is not available for some pixels; in these cases the pixel is replaced by an exception value, which is a small negative number the value of which gives information about the particular fault encountered. Some of the exception conditions will only affect a particular channel; for example a particular channel may saturate, or may have no signal, while the other channels give a valid measurement. Other exception conditions may affect all channels, as when an instrument scan is missing or could not be decompressed because of CRC errors.

The exception values used to indicate faulty pixel data are shown in Table 2.17 . Note that some but not all of the exception conditions will apply to all channels. That is, if the exception value appears in one channel for a given pixel, it will apply to all, for example if the scan is not decompressed. On the other hand, a condition such as saturation or no signal in channel may affect on channel bit not the others.

Table 2.17 also gives the corresponding confidence word bit in each case.

Table 2.17 Pixel exception values in GBTR MDS #1 to MDS #14

Exception Value

Meaning

confidence word bit

-1

Scan Absent (null packet)

2

-2

Pixel Absent

3

-3

Not decompressed

4

-4

No signal in channel

5

-5

Saturation in channel

6

-6

Derived radiance outside Calibration

7

-7

Calibration Parameters unavailable

8

-8

Unfilled Pixel (set by cosmetic fill algorithm)

9

The confidence words contain a series of flags for each pixel. Separate flags are provided for the nadir and forward views. The GBTR confidence flags are listed in Table 2.18 .

The blanking pulse flag (bit 1) indicates that one of the radar instruments was transmitting at the time of the pixel measurement. It is provided so that if there were any interference between the radar s and AATSR it would be possible to identify affected pixels.

Bit 2 is set to indicate a cosmetic fill pixel. Note that the allocation of cosmetic fill pixels is determined entirely on geometrical considerations, so that a cosmetic fill pixel may show an exception value if the neighbouring pixel from which it is copied does.

Bits 2 - 9 are derived from the pixel exception values. In each case the bit is set if the corresponding exception value is set for any of the channels. Thus in cases where only one value is affected by the exception value, the bit may be set even though some of the channels contain valid data.

Table 2.18 GB TR Confidence Flags (nadir or forward view)
.

Bit

Meaning if set

0

Blanking Pulse

1

Cosmetic Fill Pixel

2

Entire scan absent from telemetry

3

Pixel absent from telemetry

4

Pixel not decompressed owing to error in packet validation

5

No signal in some channel (zero count)

6

Saturation in some channel (maximum count)

7

Derived radiance of some channel outside range of calibration

8

Calibration Parameters unavailable for pixel

9

Pixel unfilled (cosmetic fill algorithm unable to find nearest neighbour pixel)

10 - 15

Unused

Note: Bits are numbered from ms bit 15, ls bit 0

The cloud / land flag words contain the cloud and land flags for each pixel. Separate flags are provided for the nadir and forward views, since several of the cloud tests are applied to the forward and nadir view images separately, and may give different results for any pixel. These flags are listed in Table; their meaning is largely self-explanatory.

Table 2.19 GBTR Cloud-clearing/land flagging flags (nadir or forward view)
.

Bit

Meaning if set

0

Pixel is over land

1

Pixel is cloudy (result of all cloud tests)

2

Sunglint detected in pixel

3

1.6 micron reflectance histogram test shows pixel cloudy (day-time only)

4

1.6 micron spatial coherence test shows pixel cloudy (day-time only)

5

11 micron spatial coherence test shows pixel cloudy

6

12 micron gross cloud test shows pixel cloudy

7

11/12 micron thin cirrus test shows pixel cloudy

8

3.7/12 micron medium/high level test shows pixel cloudy (night-time only)

9

11/3.7 micron fog/low stratus test shows pixel cloudy (night-time only)

10

11/12 micron view-difference test shows pixel cloudy

11

3.7/11 micron view-difference test shows pixel cloudy(night-time only)

12

11/12 micron thermal histogram test shows pixel cloudy

13-15

Unused

Note: Bits are numbered from ms bit 15, ls bit 0

Full details of the format are here 6.2.1. .

The Level 1B annotation data sets include geolocation data (pixel latitude and longitude), topographic data, solar and viewing angles, and data to show the mapping between the image and instrument pixels.

The format of the Summary Quality ADS is described here 6.6.45. .

The remaining ADS contain one record per granule in the along track direction and are conceived so that interpolation error should not be a significant problem.

ADS 1 and ADS 2 are provided so that the original scan positions can be recovered if required. They are an FODP Ref. [1.3 ] Annex B requirement.

ADS 3 6.6.43. contains grid pixel latitude and longitude. These do not need to be much better than the equivalent of 1 km (the nominal pixel size).

ADS 4 6.6.44. contains scan pixel x and y. These are of supplied for specialist users who want to know by how much the pixels have been displaced in the regridding.

ADS 5 and ADS 6 contain solar and viewing angles for pixels in the nadir and forward view respectively. These are calculated once for each across-track band (i.e. with an across-track sampling of about 50 km).

Finally, a Visible Calibration GADS 6.6.51. contains calibration data for the visible channel, derived from the current orbit. (Note that this is not the calibration data that has been applied to the visible channel pixels of the current orbit; that will have derived from an earlier orbit.)

More information on the sampling schemes used in the ADSs listed above can be found in section 2.12.1.3.1. , Hints and Algorithms on Data Use.

2.6.2.1.2 ATS_AST_BP

The AATSR Browse Product ATS_AST_BP 6.3.1. is a 3 colour image product derived from the Level 1B product. It is sub-sampled at 4 km resolution. The product contains 2 ADS and 1 MDS.

The Browse Summary Quality ADS 6.6.45. is essentially identical to that of the Level 1B GBTR product.

ADS 1 6.6.11. contains the geolocation information from the corresponding Level 1B ADS. It is sampled at 1 record per granule, and on the same across-track tie points as the corresponding Level 1B ADS. Note that because the Browse product is sub-sampled at 4 km nominal resolution, 1 granule corresponds to 8 Browse MDS records.

The single Browse MDS 6.6.12. contains RGB image data for 128 across-track pixels.

2.6.2.2 Structure of AATSR Ungridded Products

2.6.2.2.1 UCOUNTS

The UCOUNTS product provides raw detector output (counts) in each waveband, for both thermal infrared and reflectance channels, together with calibration data from both thermal and reflectance calibration sources. End-users are unlikely to be interested in this product, it is primarily a tool for AATSR instrument scientists and engineers. Unlike the ATSR-2 UCOUNTS product, no geolocation information is provided in this product. When geolocation information is required in an ungridded product, it can be found in the UBTR.

The format and contents of the UCOUNTS product are shown in table 2.20 to table 2.22 . There are no ADS defined for the UCOUNTS product. All MDS records for all 7 channels share the same data set structure as shown in table 2.21 . The size of the UCOUNTS product is approximately 645 Mbyte/orbit.

Table 2.20 Product Structure
Data Set Data Set Records Contents
MPH MPH Record Main Product Header
SPH SPH Record
DSD for MDS #1
...
DSD for MDS #7
Specific Product Header
MDS #1 MDS Record #1
...
MDS Record n
12 µm detector record
MDS #2 MDS Record #1
...
MDS Record n
11 µm detector record
MDS #3 MDS Record #1
...
MDS Record n
3.7 µm detector record
MDS #4 MDS Record #1
...
MDS Record n
1.6 µm detector record
MDS #5 MDS Record #1
...
MDS Record n
0.87 µm detector record
MDS #6 MDS Record #1
...
MDS Record n
0.67 µm detector record
MDS #7 MDS Record #1
...
MDS Record n
0.55 µm detector record
Table 2.21 Data Sets Structure MDS #1 - #7
Field Number Field Description Units Size
1 UTC nadir time 1 days 4 bytes
2 UTC nadir time 2 s 4 bytes
3 UTC nadir time 3 µs 4 bytes
4 spare   4 bytes
5-579 nadir view pixel detector counts counts 575 x 2
580-970 forward view detector counts counts 391 x 2
  plus black body (+bb) detector counts 36 x 2
  minus black body (-bb) detector counts 36 x 2
  VISCAL unit detector counts counts 36 x 2
  VISCAL monitor diode signal   2
  mean cold black body radiance   2
  measured +bb temperatures 0.001K 7 x 4
  measured -bb temperatures 0.001K 7 x 4
  SCP gain (mantissa)   4
  SCP gain (exponent)   2
  SCP offset (mantissa)   4
  SCP offset (exponent)   2
  IDF scan count when SCP gain/offset last changed   4
  calibration gain mantissa (even pix)   4
  calibration gain exponent (even pix)   2
  calibration gain mantissa (odd pix)   4
  calibration gain exponent (odd pix)   2
  calibration offset mantissa (even pix)   4
  calibration offset exponent (even pix)   2
  calibration offset mantissa (odd pix)   4
  calibration offset exponent (odd pix)   2
  packet sequence count   4
  source packet validation result   2
  ICU on-board time   4
  IDF scan count   4
  spare   13 x 2
Table 2.22 UCOUNTS Exception Values
Parameter Value Meaning
Detector Counts -1 Entire scan absent from telemetry
  -2 Pixel count initial value
  -3 Source packet failed basic validation
  -4 No signal in channel (zero counts)
  -5 Saturation in channel (maximum counts)

2.6.2.2.2 UBTR

The UBTR (Ungridded Brightness Temperature/Reflectance) product provides calibrated thermal infrared and reflectance channel data, preserving the instrument scan geometry, but providing target lattitude/longitude and ground track x/y co-ordinates for each instrument scan sample or "pixel".

The format and contents of the UBTR product are shown in table to table 2.28 . The product is comprised of 10 ADS (table 2.24 to table 2.26 ) and 7 MDS (table 2.27 ). All MDS records for all 7 channels share the same data set structure, with the exception that the thermal channel data sets contain values of BT and the visible and NIR channels contain percentage reflectance. The size of the UCOUNTS product is approximately 665 Mbyte/orbit.

Table 2.23 Product Structure
Data Set Data Set Records Contents
MPH MPH Record Main Product Header
SPH SPH Record
DSD for ADS #1
...
DSD for ADS #10
DSD for MDS #1
...
DSD for MDS #7
Specific Product Header
ADS #1 ADS Record #1
...
ADS Record n
latitudes of nadir view pixels
ADS #2 ADS Record #1
...
ADS Record n
latitudes of forward view pixels
ADS #3 ADS Record #1
...
ADS Record n
longitudes of nadir view pixels
ADS #4 ADS Record #1
...
ADS Record n
longitudes of forward view pixels
ADS #5 ADS Record #1
...
ADS Record n
x co-ordinates of nadir view pixels
ADS #6 ADS Record #1
...
ADS Record n
x co-ordinates of forward view pixels
ADS #7 ADS Record #1
...
ADS Record n
y co-ordinates of nadir view pixels
ADS #8 ADS Record #1
...
ADS Record n
y co-ordinates of forward view pixels
ADS #9 ADS Record #1
...
ADS Record n
nadir view solar and viewing angles
ADS #10 ADS Record #1
...
ADS Record n
forward view solar and viewing angles
MDS #1 MDS Record #1
...
MDS Record n
12 µm detector record
MDS #2 MDS Record #1
...
MDS Record n
11 µm detector record
MDS #3 MDS Record #1
...
MDS Record n
3.7 µm detector record
MDS #4 MDS Record #1
...
MDS Record n
1.6 µm detector record
MDS #5 MDS Record #1
...
MDS Record n
0.87 µm detector record
MDS #6 MDS Record #1
...
MDS Record n
0.67 µm detector record
MDS #7 MDS Record #1
...
MDS Record n
0.55 µm detector record
Table 2.24 Data Set Structure: ADS #1 - #4
Field Number Field Description Units Size
1 UTC nadir time 1 days 4 bytes
2 UTC nadir time 2 s 4 bytes
3 UTC nadir time 3 µs 4 bytes
  pixel latitude or longitude deg/1000 575 x 4 (nadir)
391 x 4 (forward)
Table 2.25 Data Set Structure: ADS #5 - #8
Field Number Field Description Units Size
1 UTC nadir time 1 days 4 bytes
2 UTC nadir time 2 s 4 bytes
3 UTC nadir time 3 µs 4 bytes
  pixel x or y co-ordinate meters 575 x 4 (nadir)
391 x 4 (forward)
Table 2.26 Data Set Structure: ADS #9 - #10
Field Number Field Description Units Size
1 UTC nadir time 1 days 4 bytes
2 UTC nadir time 2 s 4 bytes
3 UTC nadir time 3 µs 4 bytes
6 - 50 solar elevation degs 11 x 4
51 - 94 satellite elevation degs 11 x 4
95 - 138 solar azimuth degs 11 x 4
139 - 182 satellite azimuth degs 11 x 4

Note: The solar and viewing angles are provided once per granule, for the following tie point pixels:

  • nadir view pixels: 574, 516, 459, 401, 344, 287, 229, 172, 114, 57, 0
  • forward view pixels: 0, 39, 78, 117, 156, 195, 234, 273, 312, 351, 390

The nadir pixels are provided in reverse order since AATSR scans the nadir view right-to-left, and the forward view left-to-right (as the scan rotates clockwise). This approach means that the angles given in these ADS are given from left-to-right, for both views.

Table 2.27 Data Set Structure MDS #1 - #7
Field Number Field Description Units Size
1 UTC nadir time 1 days 4 bytes
2 UTC nadir time 2 s 4 bytes
3 UTC nadir time 3 µs 4 bytes
4 spare   4 bytes
5-516 nadir view pixel brightness temp. or reflectance 0.01K (BT)
%/100 (refl.)
575 x 2
  forward view pixel brightness temp. or reflectance 0.01K (BT)
%/100 (refl.)
391 x 2
  plus black body (+bb) detector counts 36 x 2
  minus black body (-bb) detector counts 36 x 2
  VISCAL unit detector counts counts 36 x 2
  VISCAL monitor diode signal   2
  mean cold black body radiance   2
  measured +bb temperatures 0.001K 7 x 4
  measured -bb temperatures 0.001K 7 x 4
  SCP gain (mantissa)   4
  SCP gain (exponent)   2
  SCP offset (mantissa)   4
  SCP offset (exponent)   2
  IDF scan count when SCP gain/offset last changed   4
  calibration gain mantissa (even pix)   4
  calibration gain exponent (even pix)   2
  calibration gain mantissa (odd pix)   4
  calibration gain exponent (odd pix)   2
  calibration offset mantissa (even pix)   4
  calibration offset exponent (even pix)   2
  calibration offset mantissa (odd pix)   4
  calibration offset exponent (odd pix)   2
  packet sequence count   4
  source packet validation result   2
  ICU on-board time   4
  IDF scan count   4
  spare   13 x 2
Table 2.28 UBTR Exception Values
Parameter Value Meaning
BT/Reflectance -1 Entire scan absent from telemetry
  -2 Pixel count initial value
  -3 Source packet failed basic validation
  -4 No signal in channel (zero counts)
  -5 Saturation in channel (maximum counts)
  -6 Derived radiance outside calibration range
  -7 Calibration unavailable for pixel
  -8 Pixel unfilled