IOD Observation Format Description

Positional observations of satellites provide the basis to determine their orbits, and to study their optical characteristics. The latter provide the basis for the accurate brightness predictions that we have come to expect from our favourite prediction software or service.

Positional observations are analysed using computer programs, so observers need a systematic and accurate reporting format, ideally one that can be read by both humans and machines. The IOD (Interactive Orbit Determination) format is one of several that meet this need.

George D. Lewis developed the IOD observation format, and a supporting data-entry program, called ObsEntry, available here.

Below is a reproduction of the description of the IOD format, that is included with ObsEntry.

		Interactive Orbit Determination (IOD) Version 0

			       George D. Lewis

				10 October 1998

			 Copyright (C) 1998, G. Lewis


		   IOD Observation Format Description

			     Clarified 24 Feb 2002
	  (more realistic examples, cols 32-40, 42-43, 48-54, 56-61)


--------------------------------------------------------------------------------
	10        20        30        40        50        60        70        80
123456789 123456789 123456789 123456789 123456789 123456789 123456789 123456789

					       AAAAAAA+EEEEEE
		       YYYYMMDDHHMMSSsss tt ce RRRRRRR-DDDDDD pp
12345 98 123XYZ 2007 S 19981122112233444 56 14 1122334-112233 46 B+MMm Mm SSSsss

Examples:
12345 98 123A   2007 G 20081122112233444 56 14 1122334+112233 39 S
12345 98 123A   2007 F 2008112211223344  56 25 1122   +1122   28 R+05  1
12345 98 123A   2007 P 200811221122334   27 35 11223  +112    27 S+070 10
12345 98 123LEO 2007 B 20081122112233    18 75 1122334+112222 36 V+110 1
12345 98 123UNK 2007 F 200811221122000   27                      B-005 05
12345 98 123UNK 2007 F 20081122112233444 28                      V+095 05
12345 98 123UNK 2007 F 200811221123400   27                      P-010 05  10000
		2007 O 20081122
		2007 C 200811231130

--------------------------------------------------------------------------------


Cols   1- 15: Object number and international designation.

Cols  17- 20: Four digit station number.

Col       22: Station status code.

	      Sky condition codes:

	      E = excellent: no Moon/clouds, great seeing, minimal air/light pollution
	      G = good     : no Moon/clouds, conditions could be better, but not much
	      F = fair     : young/old Moon, some air/light pollution making fainter stars invisible
	      P = poor     : gibbous Moon, haze, more air/light pollution making more stars invisible
	      B = bad      : bright Moon, air/light pollution, some clouds; difficult
	      T = terrible : bright Moon, air/light pollution, looking through clouds

	      Station status codes:

	      C = clouded out
	      O = sky clear, but observer not available

	      The purpose of the 'C' and 'O' codes is to enable reporting of
	      "station unavailable" status to a network coordinator.

Cols  24- 31: UTC date. Four digit year, two digit month and day of month.

Cols  32- 40: UTC time. Two digit hour and minute. Seconds are reportable to
	      a precision of 0.001 second (same as TLE precision). NON-SIGNIFICANT
	      DIGITS MAY BE ZERO (0), NON-ZERO (1-9) or BLANK. The whole field
	      may be blank if no time reported when using station status codes.
	      Expected accuracy is stated using cols 42-43.

Cols  42- 43: Time uncertainty. Omit if no time reported or station status codes
	      used. Expressed as MX, where M = mantissa, and X = exponent input.
	      Evaluated as M*10E(X-8). Examples:

			     MX = 15: 1*10E(5-8) =   0.001 sec
			     MX = 56: 5*10E(6-8) =   0.05  sec
			     MX = 17: 1*10E(7-8) =   0.1   sec
			     MX = 97: 9*10E(7-8) =   0.9   sec
			     MX = 18: 1*10E(8-8) =   1     sec
			     MX = 28: 2*10E(8-8) =   2     sec
			     MX = 58: 5*10E(8-8) =   5     sec
			     MX = 19: 1*10E(9-8) =  10     sec
			     MX = 29: 2*10E(9-8) =  20     sec
			     MX = 99: 9*10E(9-8) =  90     sec  (largest)

Col       45: Angle format code. BLANK IF NO POSITION IS REPORTED.
	      To allow for user preference, four RA/DEC and three AZ/EL
	      formats are provided. The first six of these are the same
	      formats as used in the OTWG system, with the exception that
	      one less digit of precision is available in both position
	      coordinates. Positional coordinates are reported in columns
	      48-61. The positional uncertainty is reported in columns 63-64.
	      The seven positional formats are:

				     50        60
				    89 123456789 1234

		 Format 1: RA/DEC = HHMMSSs+DDMMSS MX   (MX in seconds of arc)
			2: RA/DEC = HHMMmmm+DDMMmm MX   (MX in minutes of arc)
			3: RA/DEC = HHMMmmm+DDdddd MX   (MX in degrees of arc)
			4: AZ/EL  = DDDMMSS+DDMMSS MX   (MX in seconds of arc)
			5: AZ/EL  = DDDMMmm+DDMMmm MX   (MX in minutes of arc)
			6: AZ/EL  = DDDdddd+DDdddd MX   (MX in degrees of arc)
			7: RA/DEC = HHMMSSs+DDdddd MX   (MX in degrees of arc)


Col       46: Epoch code. BLANK IF AZ/EL.

	      0 or blank = of date
	      1 = 1855
	      2 = 1875
	      3 = 1900
	      4 = 1950
	      5 = 2000
	      6 = 2050

Cols  48- 54: Observed RA or AZ. NON-SIGNIFICANT DIGITS MAY BE ZERO (0),
	      NON-ZERO (1-9) or BLANK. Expected accuracy is stated using
	      cols 63-64.

Col       55: DEC or EL sign

Cols  56- 61: Observed DEC or EL. NON-SIGNIFICANT DIGITS MAY BE ZERO (0),
	      NON-ZERO (1-9), OR BLANK. Expected accuracy is stated using
	      cols 63-64.

Cols  63- 64: Positional uncertainty. Expressed as MX, where M = mantissa,
	      and X = exponent input. Evaluated as M*10E(X-8). Given in seconds,
	      minutes, or degrees of arc according to the format used. Assumed
	      to apply equally to both components.

	      Examples of positional uncertainty ("/" = "or"):

		     MX = 34  3*10E(4-8) =  0.0003 deg/min/sec of arc
		     MX = 56: 5*10E(6-8) =  0.05   deg/min/sec of arc
		     MX = 17: 1*10E(7-8) =  0.1    deg/min/sec of arc
		     MX = 97: 9*10E(7-8) =  0.9    deg/min/sec of arc
		     MX = 18: 1*10E(8-8) =  1      deg/min/sec of arc
		     MX = 28: 2*10E(8-8) =  2      deg/min/sec of arc
		     MX = 58: 5*10E(8-8) =  5      deg/min/sec of arc
		     MX = 19: 1*10E(9-8) = 10      deg/min/sec of arc
		     MX = 29: 2*10E(9-8) = 20      deg/min/sec of arc
		     MX = 99: 9*10E(9-8) = 90      deg/min/sec of arc (largest)


Col       66: Optical behavior code. BLANK IF NO DATA.

	      Optical Tracking Working Group Codes:

	      E = unusually faint because of eclipse exit/entrance
	      F = constant flash period
	      I = irregular
	      R = regular variations
	      S = steady
	      X = irregular flash period

	      Flash Period Codes:

	      B = time zero for averaging several flash cycles
	      H = one flash in a series
	      P = end time for averaging several flash cycles. Time interval
		  from last "B" report divided by flash period reported on
		  this line gives number of flashes that occurred since "B".

	      Miscellaneous Visibility Codes:

	      A = became visible (was invisible); use E for eclipse exit
	      D = object in field of view, but not visible
	      M = brightest
	      N = faintest
	      V = best seen using averted vision


Cols      67: Visual magnitude sign.  BLANK IF NO DATA.

Cols  68- 70: Visual magnitude. Implied decimal point
	      between cols 69 and 70. BLANK IF NO DATA.

Cols  72- 73: Magnitude uncertainty. Implied decimal point
	      between cols 72 and 73. BLANK IF NO DATA.

Cols  75- 80: Flash period in seconds. Implied decimal point
	      between cols 77 and 78. BLANK IF NO DATA.

Links to: The VSO Home Page, Positional Measurements, Position Formats.

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