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.