Subject: Comparison between old and new ionospheric corrections
From: "Cerri Luca" <[email-masked]>
To: <[email-masked]>
Cc: "Frank Lemoine" <[email-masked]>
Date: Tue, 5 Jun 2007 18:45:07 +0200

Dear all,

Here follows a brief summary of the tests that we performed 
using the new ionospheric correction for Doris measurements 
(see DorisMail No 0498, may 25, 2007). 

All the tests have shown that the difference between two orbits 
determined with the old and new ionospheric corrections is less than 
1 mm in radial, along track, and cross track components.
As an example you fill find an orbit comparison for Envisat arc 166 
and jason cycle 37 (time is in days).

Few tests were performed by solving for station coordinates with a
multi-satellite 
configuration on three-day arcs. Results indicate a difference 
between the two sets of coordinates (old Vs new ionospheric correction) 
in the order of 1 mm.

Arc Nr.   Mean Day of arc  Mean 3D RMS (mm) Nr of stations    satellites
1           26/05/07           1.6             50          envis1 spot5
spot4
2           27/05/07           1.0             50          envis1 spot5
spot4
3           28/05/07           0.2             50          envis1 spot5
spot4
4           30/05/07           0.7             51          envis1 spot5
spot2 spot4
5           31/05/07           2.3             51          envis1 spot5
spot2 spot4
6           01/06/07           2.1             51          envis1 spot5
spot2 spot4

The interest of the new ionospheric correction is that it is 
independent from the frequency bias per pass that is usually estimated. 
It only depends on measured quantities (cycle counts on the the two 
frequencies, 2GHz and 400 MHz), therefore it can be calculated for any 
couple of measurements. This allows to deliver a meaningful correction 
even for completely invalidated passes, thus increasing the total number

of measurements delivered to final users. 

Best regards 

Luca

__________________________________
Luca CERRI
Centre National d'Etudes Spatiales
DCT\SB\OR
18, av Edouard Belin
31401  Toulouse Cedex 09 - FRANCE
tel.   +33 (0)5 61283549
fax    +33 (0)5 61281855
bpi    1323
email  [email-masked]