WMOD00296 ‎(2)‎

• Contract/Permit #: 14-06-D-5640
• Title: Park Range Atmospheric Water Resources Program Final Report
• Date: 9/30/1969
• Weather Modification - Doc Type: Report

..,.

Fairly light wind gusts can deposit (remove) a considerable amount of snow
on (from) the sampling sheet. The height of the sampling box is a compro-
mise, based on experience, between getting too close to the surface and
collecting large amounts of blowing snow, and getting above the surface
and getting into a serious collection problem, i. e., having snow blown past
or off of the collection sheet. All other errors in the system are small.
A second, occasionally significant source of error is that of time coordin-
ation between the two samplings. During high rates, a small time discrep-
ancy in the times of the samples being compared can introduce considerable
error. This source of error, though, is usually small compared to the wind-
caused error.

~

For the purpose of calibration the mass of snow collected on a plastic sheet
has been converted to thousandths of an inch of precipitation. Likewise, the
integral of the output signal of the optical snow rate sensor has been con-
verted to the same units. This has been done using a linear conversion be-
tween the sensor output and precipitation rate derived from earlier independ-
ent calibration data.

r = O. 3d

where

r is precipitation rate - in/hr

d is recorder deflection - milliamperes

The. correlation coefficient between over 400 collected short period samples
-_._-~-- --- - - --
and 2.p.ti~~~Ll,-eQ.~or ~ndJ~ations, spanl!,ing a ve!y wide range of snowfall con-
ditions, !~ O~.80 (~ti:p.s9D 1~68~. Table 4 gives the correlation coefficients
for these data, stratified by temperature and wind speed.

~

TABLE 4

Correlation Coefficients Between Optical Sensor Indications and Collected
Snow Totals

Wind Speed
( MPH)

o

2

4

6

8

10

12

14

16

18

Correlation
Coefficient

o. 93 O. 91 O. 87 O. 96 8. 82 O. 85 O. 53 O. 72 O. 64 O. 79

3

Temp. OF
Corr. Coef.

5 10 15
0.100.82

20 25 30 35
O. 70 O. 74 O. 88 O. 94 O. 27

32