Subject: [IGSMAIL-321] Accuracy code in EMR files
From: Jan Kouba
Date: 20 AUG 1993 15:29:28

IGS Electronic Mail       20-AUG-1993 15:29:28       Message Number 321
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From: Jan Kouba 
Subj: Accuracy code in EMR files
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 This is to notify our IGS colleagues about the change we have adopted 
 starting with the week 709. Namely, we are now putting the accuracy estimates
 in the sp3 headers (lines 8-12). We were inspired to do so by Geoff Blewitt's
 recent IGS message on orbit metrics (IGS #311).
 For all orbits passing our daily quality analysis, we are assigning a binary
 exponent of 9, which, in the sp3 convention (see NOAA Technical Report NOS 133
 NGS 46), translates to a sigma of 
                      2**9= 512mm.
 For the orbits failing our daily analysis we are arbitrarily assigning sigmas
 derived as follows:
	              abs( est. error)/4
 This, we feel, is a better alternative than searching the summary files to 
 identify anomalous satellites and to decide which satellite should be avoided
 for further analysis/comparisons.
 Furthermore, approximate orbit errors (ranges of absolute values) can
 still be recovered from the orbit accuracy code. Below are the codes and the 
 corresponding ranges of orbit sigmas as specified by the sp3 convention:
   
            sigma                           sp3 accuracy code (exponent of 2)
                  <   0.384m                           8
           0.385m to  0.768m                           9  NORMAL ORBITS
           0.769m to  1.536m                          10
           1.537m to  3.072m                          11
           3.073m to  6.144m                          12
           6.145m to 12.288m                          13
           12.29m to 24.58 m                          14
	   24.58m to 49.15 m                          15
	   49.15m to 98.30 m                          16
		  >  98.30 m                          17  DO NOT USE

 Greetings from the EMR team!