Readme.txt

The ground-satellite comparison summary table and plot/statistics files for Dobson,
Brewer and Filter instruments.

For the summary table, the available data are binned into five periods 

1978-1985,
1986-1990,
1991-1995,
1996-2000,
2001-2006

and various statistics of the ground-based vs. satellite
difference were calculated for each bin. 

These statistics are:

- the mean difference for each bin,
- the standard deviation of daily ground-satellite differences in %,
- standard deviations of monthly mean differences,
- the amplitude of the annul cycle in the difference,
- the range (i.e., max. value minus min. value) of the annual mean differences.

The distribution of all these statistics have also been calculated. Based on that, the "suspect"
and "outliers" were defines as values that are outside approximately the 90th and 95th
percentiles respectively. The same percentile limits were used for all types of
instruments, although they were determined from Dobson and Brewer data only. In other
words, Filter data were judged based on the same criteria as Dobsons and Brewers.

The DS_summary.pdf file contains the estimates for each station for all 5 bins. Five
symbols for each bin represent the outcome of 5 statistics estimate. The "suspect" values
are shown as blue dots, potential "outliers" are in red. The last column represent the
range on mean values for the five bins. If this range is above a certain limit, the
record is marked as a "suspect" or "outliers". The records are sorted by the instrument
type and then by latitude from south to north.

The station-by-station comparison results in 4 other attached files. For each station,
they contain a plot of the ground-satellite difference, the statistical summary table and
Ulf's intercomparison recommendation table (for Dobson data). The plots show seasonal
mean differences (Ground-satellite)/Ground in %. The read line is for DS observations.

The mean values are joined by a solid line. The vertical lines show a 95% confidence
limit for the mean. Differences for all other type of observations are shown in blue. The
vertical green lines indicate instrument changes. The instrument numbers are on the top.

The instrument intercomparison dates are marked by vertical green dashes lines. The
stations are sorted by latitude from south to north. The Summary table contains the
actual values of the five statistics for each bin.


Instrument calibration information is also available from the WOUDC web site.  Refer to the
Data Archive Search Form at: http://www.woudc.org/data/MetaQuery/metaquery_e.cfm

Select the instrument type you wish to review (Ex. Dobson) and check the Model and Number boxes.
Then submit.  Those instruments with highlighted links have calibration information posted.