WMOD00511

• Title: Precipitation Guage Testing on the Wasatch Plateau, Utah, During Early 1993
• Date: 11/1/1993
• State: UT
• Weather Modification - Doc Type: Report

INTRODUCTION

Field observations were made to test an ETI (Electronic Techniques, Inc.) precipitation gauge
at the High Altitude Site on the western slope of the Wasatch Plateau in central Utah, east
of Fairview. The ETI gauge should require little servicing because it is designed to
automatically discharge its precipitation and antifreeze mix when gauge capacity is reached.
The gauge then automatically recharges itself with antifreeze. It provides digitized data at
a resolution of 0.01 in., which can be transmitted from remote locations. The ETI gauge
could provide a desirable alternative to conventional recording gauges in several applications,
including evaluation of cloud seeding projects, if it performs as advertised. The testing
program was intended to determine its performance in a winter mountain environment.

The tests were conducted in a small clearing within a conifer forest at latitude 390, 37',
longitude 1110,22', elevation 8200 ft. The site is rated "over-protected" because of the close
proximity of trees of an estimated height near 70 ft all around the clearing. However, the
site was convenient to service while testing other instrumentation in a nearby open area, and
was satisfactory for comparison of precipitation gauges and snowboards.

The test period ran from 1400 (all times m.s.t.) on February 16, 1993, until 1000 on March
28, 1993. Data collected earlier have not been analyzed because the Alter windshield on the
Belfort weighing gauge was several inches too high until the stated start time. That height
may not have been important in the very protected clearing, but adequate data exist after
the shield top was adjusted to be near level with the gauge orifice top.

OBSERVATIONS

Three precipitation sensors were compared as listed below:

1. An ETI gauge was operated with its orifice about 10 ft above ground level. The gauge had
a 12-in. diameter orifice and was supplied with a windshield similar to an Alter shield but
made of heavy-duty, fixed plastic panels. This load cell gauge was electronically interrogated
every 15 min by a Campbell CR-10 data logger. The manufacturer's stated gauge resolution
was 0.01 in. snow water equivalent.

2. A standard Belfort universal weighing gauge with 12-in. capacity was operated with an
11-5/16-in. orifice (twice the area of the standard 8-in. orifice). This reduced the gauge
capacity to 6-in. but doubled the resolution to 0.005 in. The larger orifice also essentially
eliminated gauge "capping" by snow buildup on the sloping sides below the orifice. An Alter
windshield was used with this gauge. The Belfort gauge was located about 10 ft horizontally
from the ETI gauge. The orifice height above ground was the same for both gauges. The
Belfort's electric chart drive was geared to rotate once per 24 h, providing a time resolution
better than 5 min. The chart time was checked frequently during the test period. The chart
traces were carefully read with the aid of magnification to the nearest 0.01 in. chart scale,
equivalent to 0.005 in. resolution with the orifice used. This gauge was carefully calibrated
with standard weights before field use, and the calibration was rechecked after installation.
In practice, the gauge chart was always changed before the gauge reached the midway
turnaround point (6 in. on the chart). This procedure eliminated recording beyond that point
where this type of gauge is less accurate.