NSA/SONDE/C1 - Reprocessed: Incorrect surface altitude

The value of the station altitude (relative to mean sea level) is
incorrect in all NSA radiosonde files prior to 2/14/2004.  The correct
value is 8 m.  The incorrect value can be different.  Prior to 4/24/2002
(in platform nsaisssonde...) it was given as 12 m.  From 4/24/2002 to
2/13/2004 (in platform nsasondewnpn...) it is almost always given as
27 m (sometimes [rarely] 17 m).

Because the altitude computation is based on the pressure measurement
the error is linear.  A general method to correct the problem is outlined
in the following pseudocode:

SET SurfAlt = 8.
GET Array_of_alt_values
SUBSTRACT first alt_value from all alt_values
ADD SurfAlt to alt_values

Reprocessed nsaisssondeC1.a1 and nsaisssonde10sC1.b1 data archived 20070702

• -180.0 - +180.0(alt)

• -180.0 - +180.0(alt)