OBS File Structure

27AUG22 original
Contents

Overview

An OBS file contains an Observation List, a set of geometric tangent point altitudes together with associated time data. These can be used to simulate L1B data for the Cubemap Instrument Bypass as a more realistic alternative to a regularly spaced altitude grid.

Example: 580_40_equi.obs, which can be read with IDL function read_obs.pro

File Structure

The file contains a single header record, which is ignored, followed by an arbitrary number of data records representing measurements in time order.

The data ends when the end-of-file is detected.

Header Section
HDR Header record (ignored)
Data Section
DO UNTIL [eof]
    TIM(i) RAD(i) SAT(i) HGT(i) Data for Observation i

Data Dictionary

Field Type Description Units Range
HDR String*80 Header record
HGT Double(*) Tangent height km 0–120 expected
RAD Double(*) Earth radius at tan.pt km 6300 – 6400 expected
SAT Double(*) Satellite vector km ≥ 6800 expected
TIM Double(*) Time Stamp Julian Day[1] > 2450000 expected

Notes

  1. Time is in Absolute Julian Day (ie since 4713 BC) which is converted to Day since 01 Jan 2000 (=0) on input for consistency with the definition used elsewhere

Document Changes

27AUG22 Original