NOAA Polar Orbiter Data User's Guide

Section 4.3

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4.3 MSU Data

This section describes the Microwave Sounding Unit (MSU), its data characteristics, and magnetic tape formats. Section 4.3.1 contains a description of the instrument and its data characteristics. Section 4.3.2 describes the tape formats for full data set copies, 16-bit unpacked format, and selective extract subsets.

4.3.1 Instrument Description and Data Characteristics

MSU is a microwave spectrometer that uses a four-channel Dicke radiometer making passive measurements in the 5.5 millimeter oxygen region. The four channels respond to the following respective spectral frequencies: 50.3, 53.74, 54.96, and 57.95 GHz with a channel bandwidth of 200 MHz in each case, and a typical NEΔT of 0.3K. The MSU sensors consist of two four-inch diameter antennas, each having an IFOV of 7.5 degrees. The antennas are step-scanned through eleven individual 1.84-second Earth viewing steps and require a total of 25.6 seconds to complete. The 124-kilometer IFOV resolution at the subpoint creates an underlap of approximately 115 km between adjacent scan lines. See Table 4.0-1 .

The MSU data output represents an apparent brightness temperature after a 1.84-second integration period per step. The data is quantized to 12-bit precision and combined with telemetry and step position information to produce an effective output data rate of 320 bits per second.

Unlike the HIRS/2 and SSU instruments, the MSU has no special calibration sequence that interrupts normal scanning. The calibration data is included in a scan line of data. From the last Earth view position, the reflector rapidly moves 4 steps to view space, 10 additional steps to view the housing, and then returns to the home position to begin another scan line. Since each scan line requires 25.6 seconds, synchronization of MSU within the other two TOVS instruments occurs every 128 seconds (5 scan lines).

4.3.2 Magnetic Tape Formats

The data set format for full data set copies (all channels) is different from the format for selective extract subsets (selected channels). Sections 4.3.2.1 and 4.3.2.2 contain formats for MSU full data set copies and MSU selective extract subsets, respectively. Section 4.3.2.1 also includes the unpacked format for MSU data (all channels).

4.3.2.1 Full Data Set Copies

Each MSU data set normally contains an individual satellite recorder playback. Data within each MSU data set are in chronological order with one record for each MSU scan. Each record is written in binary and contains 437 bytes (440 bytes prior to January 1, 1995). Table 4.3.2.1-1 contains the format for the MSU data.

Table 4.3.2.1-1. Format of MSU data.
Byte # # Bytes Content
1-2 2 Scan Line
3-8 6 Time Code
9-12 4 Scan Quality Indicators
13-16 4 Earth Location Delta
17-112 96 Calibration Coefficients
113-116 4 Height and Local Zenith Angle
117-160 44 Earth Location Data
161-384 224 MSU Data
385-400 16 Scan Position Quality
401-437 (440 prior to 1/1/1995) 37 (40 prior to 1/1/1995) Spare

The scan line, time code, and height and Local Zenith Anglefields have the same format as the HIRS/2 data in Section 4.1.2 .

The scan quality information is stored in four bytes. The first two bytes contain processing detected conditions, the third byte contains DACS quality indicators, and the last byte is spare. The scan quality indicators contain a summary of the quality of the 256 TIP minor frames which make up a MSU scan. The definition of the quality bytes is contained in Table 4.3.2.1-2.

Table 4.3.2.1-2. Format of the MSU scan quality bytes.
Byte Bit Definition
9 7 FATAL FLAG - Data should not be used for product generation.
6 DATA GAP - A data gap of one or more scans precedes this scan.
5 DATA FILL - This scan contains partial data fill due to missing data. Each halfword of fill is set to hex "7FFF".
4 DWELL - Data gap and/or data fill was due to dwell data.
3 TIME ERROR - This scan contains data that is suspect due to time error(s).
2 DACS - This scan contains data that is suspect due to DACS QC.
1 NO EARTH LOCATION - Earth location data not available.
0 EARTH LOCATION DELTA - Predicted less actual time exceeds tolerance of 3 seconds.
10 7 CALIBRATION - Insufficient data was collected to calibrate this scan, for at least one channel. If calibration coefficients are available, they will be old coefficients.
6-5 SPARE
4 SCAN DISABLE - The scan disable condition was detected during this scan. Normal Earth scanning was disrupted. Scan line is suspect.
3 SCAN SEQUENCE - A scan mirror sequence error was detected during this scan.
2 MIRROR SEQUENCE - A mirror sequence error was detected during this scan.
1-0 SPARE
11 7 BIT SYNC STATUS - Drop lock during this scan. Scan line is suspect.
6 SYNC ERROR - Frame sync word error greater than zero during this scan.
5 FRAME SYNC LOCK - Frame sync lock during this scan.
4 FLYWHEELING - Flywheeling detected during this scan.
3 BIT SLIPPAGE - Bit slippage detected during this scan.
2 TIP PARITY - DACS TIP parity detected during this scan.
1 AUXILIARY FRAME SYNC ERRORS - The number of bit errors in auxiliary frame sync was non-zero during this scan.
0 SPARE
12 7-4 MAJOR FRAME COUNTER
3-0 SCAN SEQUENCE COUNTER - Number (0-4) of scan position within the 128-second cycle.

The Earth location delta field contains the time differences between the scan time code and the time code associated with Earth location data appended to this record. The value, in milliseconds, is right-justified in the four bytes.

The calibration coefficient field contains two groups of calibration coefficients. Each group contains coefficients for all four channels. The first group of 32-bytes contains the calibration slope and intercept coefficients stored in ascending order. Each value is stored in four bytes and contains a scaled number of fractional bits. The scaling factor for the lowest order coefficients, the constants, is 222, with increasing order coefficients scaled by 230, 244, and 256, respectively. See Section 4.5 on how to use MSU calibration coefficients. The coefficients for MSU are stored as shown in Table 4.3.2.1-3.

Table 4.3.2.1-3. Order of MSU calibration coefficients.
Channel 1 slope coefficient (1st order term)
Channel 1 intercept coefficient (0th order term)
Channel 2 slope coefficient (1st order term)
...
Channel 1 normalization coefficient 1 (0th order term)
Channel 1 normalization coefficient 2 (1st order term)
Channel 1 normalization coefficient 3 (2nd order term)
Channel 1 normalization coefficient 4 (3rd order term)
Channel 2 normalization coefficient 1 (0th order term)
...

The Earth location field contains the latitude and longitude for each of the 11 Earth FOVs in the scan. The latitude and longitude values are stored in two-byte fields in 128ths of a degree. The order of this data is: FOV 1 latitude, FOV 1 longitude, FOV 2 latitude, FOV 2 longitude, etc.

The MSU data is extracted from the TIP frames (256 TIP minor frames per MSU scan), all zero words are discarded, and the meaningful 224 bytes (112 halfword groups) are organized by scan position and placed in the Level 1b MSU data set as shown in Table 4.3.2.1-4.

Table 4.3.2.1-4. Format of MSU data.
TELEMETRY EARTH VIEW
Scan Spot Instrument Voltages Instrument Temperature Instrument Temperature. Channel 1
Data
Channel 2
Data
Channel 3
Data
Channel 4
Data
Scan Position Line Count (2)
1 INSTR. SER. #
[0]
T1 CAL LO
[1]
T2 CAL LO
[2]
CH.1 DATA
[3]
CH.2 DATA
[4]
CH. 3 DATA
[5]
CH. 4 DATA
[6]
SCAN POS 0
SCAN CT [7]
2 E CAL LO [8] T1 CAL HI T2 CAL HI " " " " SCAN POS 1
SCAN CT [15]
3 F CAL HI [16] OTHER 1 TEMP OTHER 2 TEMP " " " " [23]
4 XTAL 1+ [24] LO 1 TEMP LO 2 TEMP " " " " [31]
5 XTAL 1- [32] LO 3 TEMP LO 4 TEMP " " " " [39]
6 XTAL 2+ [40] DICKE LOAD
1 TEMP
DICKE LOAD
2 TEMP
" " " " [47]
7 XTAL 2- [48] DICKE LOAD
3 TEMP
DICKE LOAD
4 TEMP
" " " " [55]
8 XTAL 3+ [56] TARGET 1A
TEMP
TARGET 1B
TEMP
" " " " [63]
9 XTAL 3- [64] TARGET 2A
TEMP
TARGET 2B
TEMP
" " " " [71]
10 XTAL 4+ [72] ANTENNA 1 BEARING TEMP ANTENNA 2 BEARING TEMP " " " " [79]
11 XTAL 4- [80] MOTOR TEMP MOTOR TEMP " " " " [87]
SPACE VIEW -15 +5 VOLTS
[88]
RF CHASSIS RF CHASSIS " " " " [95]
BLACKBODY VIEW +5 VOLTS
[96]
PROG TEMP PROG TEMP " " " " SCAN POS 12 SCAN CT [103]
SCAN TO SPOT #1 E ZERO
[104]
PROG TEMP [105] PROG TEMP [106] CH 1 REF [107] CH 2 REF [108] CH 3 REF [109] CH 4 REF [110] SCAN POS X SCAN CT [111]
Note: All 12-bit words; 112 words = 1 scan line = 25.6 seconds. Counts to 5 and resets every 128 seconds. Numbers in brackets[ ] indicate the halfword number.

The bit description for the MSU data is described in Tables 4.3.2.1-5 and 4.3.2.1-6 .:

a) Typical Format for all words except Scan Position-Line Count is described in Table 4.3.2.1-5.

Table 4.3.2.1-5. Typical format for all MSU words (except scan position-line count).
Bit position Description
1 (MSB) = 1 when word is a "real" word;
= 0 only for an "all zero" word.
1 = 1 when it is the first word in a scan;
= 0 at all other words.
0 = 0 for the first 6 words.
Z = 1 when in zero reference disable mode;
= 0 at all other times.
D11 Data
D10 Data
D9 Data
D8 Data
D7 Data
D6 Data
D5 Data
D4 Data
D3 Data
D2 Data
D1 Data
D0 (LSB) Data

b) Scan Position - Line Count (Word 7) is described in Table 4.3.2.1-6.

Table 4.3.2.1-6. Format of MSU scan position - line count (Word 7).
Bit Position Description
1 (MSB) = 1 when the word is a "real" word
0 = 0 when this is not the first word in a scan.
1 = 1 when this is the 8th word in the scan position.
Z = 1 when in zero reference disable mode.
S = 1 when in scan disabled mode;
= 0 at all other times.
R2 Scan line count (reset by 128 sec sync).
R1 Scan line count
R0 Scan line count
E7 Scan angle (position) data
E6 Scan angle (position) data
E5 Scan angle (position) data
E4 Scan angle (position) data
E3 Scan angle (position) data
E2 Scan angle (position) data
E1 Scan angle (position) data
E0 (LSB) Scan angle (position) data

The scan position quality is contained in 16 bytes. The first 14 bytes contain quality information for each of the 14 MSU scan positions. The last two bytes are spares. The definition of the quality byte for each scan position is contained in Table 4.3.2.1-7.

Table 4.3.2.1-7. Format of the MSU scan position quality.
Byte Bit Definition
1 7 TIME ERROR - This scan line position contains data that is suspect due to a time error.
6 MISSING DATA - The scan line position contains data fill due to a data gap. Each halfword of data fill is set to hex "7FFF".
5 DWELL - This scan line position contains data fill due to a dwell condition.
4 DACS - This scan line position contains data that is suspect due to DACS QC error(s) (DROP LOCK, SYNC ERROR, FLYWHEEL, BIT SLIP, TIP PARITY).
3 SCAN DISABLED - The instrument was in the scan disable condition during this scan line position. Normal Earth scanning is disrupted.
2 SCAN SEQUENCE - A scan sequence error was detected in this scan line position. Normal Earth scanning may be disrupted.
1 MIRROR SEQUENCE - A mirror sequence error was detected in this
0 SPARE

The 16-bit unpacked format for full copy MSU data has the same format as the "packed" data described above except for the MSU channel data field. The unpacked format for full copy MSU data for the channel data field has the format shown in Table 4.3.2.1-8. Note that the 40 bytes of spare have been eliminated and the record length is 280 bytes.

Table 4.3.2.1-8. Unpacked format for full copy MSU data (channel data field).
Byte # # Bytes Content
161-162 2 Channel 1, scan spot 1
163-164 2 Channel 2, scan spot 1
165-166 2 Channel 3, scan spot 1
167-168 2 Channel 4, scan spot 1
169-170 2 Channel 1, scan spot 2
... ... ...
247-248 2 Channel 4, scan spot 11
249-250 2 Channel 1, Space view
251-252 2 Channel 2, Space view
253-254 2 Channel 3, Space view
255-256 2 Channel 4, Space view
257-258 2 Channel 1, Blackbody view
259-260 2 Channel 2, Blackbody view
261-262 2 Channel 3, Blackbody view
263-264 2 Channel 4, Blackbody view
265-280 16 Scan position quality

4.3.2.2 Selective Extract Subsets

When channels are selected for MSU data sets, the format of the MSU channel data is the only field that changes from the format described in Section 4.3.2.1. One, two, or three channels can be selected for the MSU data sets. Table 4.3.2.2-1 shows the format of the MSU data field when Channels 1 and 4 are selected. Immediately following the MSU channel values, the scan position quality is written starting in the first available halfword.

Table 4.3.2.2-1. Format of MSU data field if Channels 1 and 4 are selected.
Byte # # Bytes Content
161-162 2 Channel 1, scan spot 1
163-164 2 Channel 4, scan spot 1
165-166 2 Channel 1, scan spot 2
167-168 2 Channel 4, scan spot 2
... ... ...
201-202 2 Channel 1, scan spot 11
203-204 2 Channel 4, scan spot 11
205-206 2 Channel 1, Space view
207-208 2 Channel 4, Space view
209-210 2 Channel 1, Blackbody view
211-212 2 Channel 4, Blackbody view

Amended April 6, 2000

Amended July 12, 2000


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