Notes on database changes to existing files:

BLANCO FILES:

[BLANCO.1983]EAST36.GPS:
While adding the 1994 Chouest Blanco data to the database, bad matches with
pre-existing data occurred.  In one particular area of overlap between 1994 
and 1983, the 1983 was +.25' of latitude offset from the new GPS data.
Not enough data (nor interest) exists to effectively shift the database at
this time.

In order to add as much of the 1994 data as possible without bad 
contouring, some cuts were made to the 1983 data.
JD 175 08:45-08:55
JD 176 01:38-01:43 and 18:17-18:23 

[BLANCO.1984]OBLN12.GPS:
During the times of ~16:17-16:24 and ~16:47-16:51 on JD 104, there are 
apparently some bad soundings within some pings.  The "bad" data appears to 
be about 200m shallower than the surrounding soundings.  Some of the most
obvious bad data was deleted and replaced with zeroes.  However a few 
suspicious contours are still evident on 100m grid contour maps.  The bad 
data was discovered while processing the 1994 Chouest Blanco data.  At this 
time no further processing was done due to time constraints.

[BLANCO.1984]OBLN16.GPS:
To best fit the 1994 Chouest data some of the 1984 data was cut:
JD101 22:40 - JD102 01:01

The 1994 data was GPS collected whereas the 1984 data was Loran shifted
to geodetic space using Lau/Fox algorithms.  

1989 BLANCO FILES-

While adding the 1994 Chouest Blanco data to the database, some cuts were
made to the existing data for a better contouring matches. (1994 data is
GPS whereas the 1989 data was Loran shifted to geodetic space using Lau/
Fox algorithms).  Offsets still exist between the shifted and true-GPS
data.  Cuts:

[GORDA.1989_B]15VENTS89.GPS:
JD 266 18:00 - 18:18

[GORDA.1989_B]16VENTS89.GPS:
JD 270 02:23 - 02:29


MENDOCINO FILES:

The Mendocino Sea Beam files collected by NOAA in 1980 used Loran-C for 
navigation.  In 1991 these files, as well as the entire NE Pacific 
spreading systems database, were shifted into geodetic coordinates using 
algorithms developed by Chris Fox and T.K. Andy Lau.  The control points 
for the Mendocino region were known to be weak in comparison to other 
areas.  In 1994, the Laney Chouest collected GPS-navigated Sea Beam across 
the Mendocino which showed the NOAA shift was in error by approximately .5 
minutes of latitude North and 1.5 to 3.0 minutes of longitude east.  New 
alogorithms were developed to re-shift the 1980 NOAA data to correspond 
geographically with the new data.  The NOAA data now matches the GPS data 
within .2 minutes of latitude/longitude.

Most of the old data was retained in the database and the new data was used 
to fill in gaps.  Much of the new data represents resurveyed areas and was 
not merged into the database.  These files are online for comparison 
studies with the clipped files used for the database are denoted by .GPS 
suffix.

The old data files for the western Mendocino were shifted and one file was 
clipped in places where the new data provided increased coverage.  The 
eastern files were not shifted as not enough information was available for 
creating a better algorithm and it appears the files were never smoothed 
for Loran roughness.  The new data was added in this part and the 
underlying old data was removed.  It should be noted that the old file is 
of questionable accuracy.

Database Files:
===============
1980 Loran-C files:             Changes:

[GORDA.1980_B]9940WX.GPS	|Newly shifted, no cuts.
[GORDA.1980_B]9940WY.GPS	|Newly shifted, some cuts.
[GORDA.1980_C]9940WY.GPS 	|Not shifted, some cuts, poorly navigated.

The above file names have been changed due to confusion of files having 
same names even though stored in separate directories.

old name			 new name
[GORDA.1980_B]9940WX.GPS        |[GORDA.1980_B]W-9940WX.GPS
[GORDA.1980_B]9940WY.GPS        |[GORDA.1980_B]W-9940WY.GPS
[GORDA.1980_C]9940WY.GPS        |[GORDA.1980_C]E-9940WY.GPS