WMOD00549

• Title: Testing of Satellite Uplinked Remote Surface Weather Stations in the Sierra Nevada
• Date: 6/19/1978
• Weather Modification - Doc Type: Report

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Project Skywater's *Environmental Data Network
by simple timeshare access. Otherwise the data
may be acquired for seasonal or long periods of
record on media such as microfiche, magnetic
tape, etc., by letter request from the Project
Skywater Data Base Manager.

6.0 CALIBRATION

A detailed shop calibration is accomplished for
all sensors to determine each mathematical rela-
tionship of a particular parameter as a func-
tion of voltage. The pressure sensor, however,
requires additional field calibration because
its range must be reset for each different site.
This field calibration is accomplished by deter-
mining a climatological midscale pressure for
the site and then measuring'the ambient pressure.
The sensor's range is approximately 3386 Pas-
cals (1 in Hg). Given the current ambient pres-
sure and the desired midscale pressure the sensor
range can be set. Next, several other ambient
pressure points and their associated voltages are
measured and a least squares fit is applied to
the measured raw pressure voltages to provide a
true raw pressure. A one-point field installa-
tion calibration is accomplished for the remain-
ing sensors by measuring the parameter and its
corresponding voltage output.

7.0 PROCESSING SOFTWARE

All of the sensor calibration equations reside in
the processing software package at the Bureau of
Reclamation's Engineering and Research Center
(ERC) in Denver, Colorado. The data received and
stored in the ERC comput~r are in raw hexadecimal
form. When the data are accessed by the user,
the date, hour and geographical group of hourly
weather stations desired must be specified. The
processing software then compares the date, time
and location of the group of surface weather sta-
tions asked for with the AESOP data base and
decides whether AESOP data are available for that
time and geographical area. If the AESOP data
are available the proper set of calibration equa-
tions (according to each different site) are used
by the software to reduce the raw data to engi-
neering units, the data are converted to the
Aviation Weather Report format, and the hourly
AESOP observation is appended to the hourly
weather group of stations asked for by the user.
Therefore, the software automatically mixes the
AESOP data with the conventional manned surface
station data whenever data are available whether
the AESOP station is in the HIPLEX program in
Montana during the summer or in the SCPP program
in California during the winter. In this way,
the user need not know the past AESOP history of
application. The user may also access the AESOP
data by itself, a day at a time, but this would
require knowledge of the AESOP application
history.

* Project Skywater Environmental Data Network is
both a real-time and post-analysis weather data
base maintained by the Bureau of Reclamation in
support of Project Skywater.

8.0 COMPARISON OF THE DATA

A comparison of manned observations versus AESOP's
observations showed the following:

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(1) Temperatures consistently compared within
:1:0.6 .C.

(2)

Dewpoint temperatures compared within :1:3 .C
in moist or precipitating situations, but
in the dryer situations the sensor was
unacceptable.

(3)

Wind speed and direction comparisons were
consistently in reasonable agreement.
There was, as would be expected, better
correlation in the higher wind situations.

(4)

Altimeter settings (pressure) compared
within :1:0.01 in Hg.

(5)

Precipitation amounts from the AESOP data
link were compared with the chart record
from the AESOP gage. Figure 3 shows the
very good agreement obtained from this com-
parison. Note that the maximum of 8-bit
resolution of the data collection platform
forces a 3.3-mm (0.13-in) minimum resolu-
tion of precipitation increments from the
AESOP. This would be a more serious con-
straint in smaller precipitation events.

250

240

230

220

210

200

120

110

100

- AESOP
- -- STANDARD CHART

90

80

70
65
o

I I I I
12 16 20 12

COORDINATED UNIVERSAL TIME (hours]

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16 2D 24

Fi(lU1'e J. Comparison of AESOP l'eported proecipita-
tion t'el'SU8 standard chart precipitation.

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