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Description of raw telemetry data file format.

Authors: A.Mazurov, E.Loupian, M.Zakharov, SMIS IKI RAN, Moscow, Russia.
e-mail: alexei@smis.iki.rssi.ru
phone: +7(095)333-5313

I. General description.

The general structure of file is as the following:

{
a. Main Header

b. Scan line header
c. HRPT Scan line telemtry data

b1. Scan line header
c1. HRPT scan line telemetry data

...

bn. Last scan line header
cn. Last HRPT scan line telemetry data.

}

where the headers are described below and every "HRPT Scan line telemtry data"
is telemetry line as it is (see "Data Extraction and Calibration of TIROS-N/NOAA
Radiometers"), but leading (first 6 * 10bit words) and trailing (last 100 *
10bit words) syncs are removed. The words are numbered according to the
reference mentioned above.

The bits inside a line are left aligned (data has been shifted 4 bit to the left - to MSB in Intel's bit/byte order).

Total length of the resulting line is 13730 bytes (size of the original line
with syncs is 11090 10bits words).

Most files contain AVHRR calibration coefficients calculated according to the
standard routine which is described in the same reference as above.

Types mentioned below:
WORD 2 bytes (16 bits) unsigned integer number
DWORD 4 bytes (32 bits) unsigned integer number
BYTE 1 byte (8 bits) unsigned integer number
char ASCII symbol (so, 1 byte)
float single precision IEEE format float number
double double precision IEEE format float number

Note: all files are prepared on IBM-PC compatible computer by software
complied using Microsoft C/C++ compiler.

II. Format description.


Main header has the following structure:

typedef struct tagUTF_HEADER
{
WORD wSize; // size of the structure
WORD utfCode; // magic word = 0x0212
WORD CalibrDone; // 1/0 if AVHRR data are calibrated/non-calibrated
DWORD dwStart; // Reserved
DWORD dwEnd; // Reserved
TRAJECTORYHEADER trjHeader; // See below
GREF gref; // See below
WORD dataCode; // Contents (instrument) ID:
// 0x0FFF -- full telemetry
// 0x0002 -- HIRS data - not fully implemented
// 0xFFFF -- unknown data (reserved)
// other values are not defined
} UTF_HEADER;

where:

typedef struct tagTRAJECTORYHEADER
{
char achSputnik[32] ; // satellite identifier (zero-terminated string)
WORD wYear ; // year A.C.
WORD wMonth ; // 1 .. 12
WORD wDay ; // 1 .. 31
WORD wHour ; // 0 .. 23
WORD wMinute ; // 0 .. 59
WORD wSecond ; // 0 .. 59 satellite tracking start time (GMT)
float fStep ; // reserved
WORD wMass ; // reserved
BYTE reserved[12] ; // reserved
WORD wExtraBytes ; // reserved
} TRAJECTORYHEADER ;

NOTE: the satellite tracking start time is a hardware operating start time to
follow satellite.

typedef struct { // ephemeris at satellite tracking start time
double time; // Epoch time (yyddd.ddddddddd).
double a; // Semimajor axis.
double e; // Eccentricity.
double incl; // Inclination.
double nodeo; // Longitude of ascending node.
double omega; // Argument of perigee.
double thetg; // Hour angle of the point of Spr/Eq.
double mo; // Mean anomaly.
double no; // mean motion
double deltat; // Time of the 1st scan line (in epoch units)
double RevNum; // Revolution number
double EphemerisType; // 1.0 - NORAD, 2.0 - TBUS
double period; //
double xndt2o;
double xndd6o;
double bstar;
double iexp;
double ibexp;
double spare1; // Clock correction (msec.) if defined.
double spare2;
double spare3;
} GREF;

The scan line header has the following structure:

typedef struct { // frame HEADER for one AVHRR scan line
WORD frm_num; // Scan line number (not used)
WORD QualContr; // Quality of line
DWORD Time; // TIME of Scan Line ( ms )
float GI[5][3]; // Array with calibration coefficients for all
channels
} stFRMHEADA;

Time - retrieved time of HRPT scan line (msec)
QualContr - quality of line (is tested during calibration):
0x000e - fine
0x0002 - time check passed
0x0004 - AVHRR PRT check passed
0x0008 - sync check passed
0x1000 - no calibration data (GI is not valuable)
GI[NChan][NCoef]:
NChan - AVHRR channel number (zero bazed; 0-4)
NCoef - 0 - gain,
1 - intercept
2 - retrieved target temperature (K)
NOTE: for visible channels only gain and intercept are available.