Background

The National Atmospheric Deposition Program (NADP) was 

established in 1977 to study atmospheric deposition and its impact 

on the environment. The program’s National Trends Network (NTN) 

includes wet atmospheric deposition networks at more than 250 sites 

across the United States, Canada, Puerto Rico, and the Virgin Islands 

(National Atmospheric Deposition Program, 2003). Precipitation 

amounts are currently measured at all NTN sites using the Belfort 

Universal Precipitation Gage 5-780 (Belfort), which involves technology that is more than 50 years old. 

In 1999, a three-phase study was begun to evaluate several weighing, all-weather precipitation gages to find a possible replacement 

for the Belfort gage. One gage that performed consistently well in 

phase I and II of the study was the OTT PLUVIO precipitation gage 

(OP). Phase III of the study was to determine the accuracy and comparability of the precipitation data collected using the OP gages and 

the existing Belfort gages. The NovaLynx Model 260-2510 Standard 

Rain and Snow Gage (NovaLynx) was used as a reference at two 

sites. Seven OP gages were installed at six NTN sites across the 

country, representing a broad range of climatic regimes, for a data 

collection period of 18 months. The six test sites were: Sand 

Mountain, Ala. (AL99), Bondville, Ill. (IL11 West and East), 

Marcell, Minn. (MN16), Smith Valley, Nev. (NV03), Penn State, 

Pa. (PA15), and Brooklyn Lake, Wyo. (WY95). A report describing 

the phase III precipitation gage evaluation is available by accessing 

<http://pubs.water.usgs.gov/wri034167>. After the phase III data 

collection period ended the NADP extended the data collection 

another six months, from January 15 through July 16, 2002. This 

fact sheet supplements the phase III report and evaluates the additional six months of data collected.

For the additional six months of data collection the OP gages at 

IL11 East and West, MN16, NV03, and PA15 were still in operation. 

As reported in the original report (Tumbusch, 2003), data-retrieval 

difficulties caused sites AL99 and WY95 to end participation in the 

study before the original 18-month data-collection period ended.

Data loss varied considerably from gage to gage (table 1). 

Mechanical difficulties were a major problem with the Belfort gages; 

the OP gages lost data because of downloading problems. The OP 

gage at PA15 had no lost data, while the corresponding Belfort gage 

lost 28 days out of 183 data collection days.

Results

A summary of test results for both the OP and Belfort gages were 

compiled for each site and are shown in tables 1 and 2. One data set 

was developed with non-event or zero data removed. Suspected 

false-positive data were removed to create another data set. An OP 

false positive was defined as a recorded response from the OP gage 

(typically 0.01) and a zero response from the Belfort gage when the 

site operator reported a zero precipitation day and there was no 

recorded opening of the NTN site sample collector. Paired t-tests 

were run on both the precipitation events and adjusted data sets, 

using a 95 percent confidence interval. Both data sets also were 

evaluated using the Wilcoxon signed-rank test (a non-parametric 

statistical test) to compare gage performance. The null hypothesis 

for the analysis was that the mean (paired t-test) or the median 

(Wilcoxon signed-rank test) difference between the gage measurements equal zero. 

Evaluation of OTT PLUVIO Precipitation Gage versus Belfort Universal Precipitation 

Gage 5-780–Supplemental Data, January 15 through July 16, 2002

For the purpose of this study, all of the data recorded by the NovaLynx 

gages were used as a reference for comparing precipitation measurements 

from gages at sites IL11 and PA15 (table 3). No data sets were removed 

for these comparisons.

Mean

precipitation,

OP/

Belfort

(inches)

0.26/0.25

0.18/0.17

0.07/0.07

0.03/0.02

0.24/0.25

Median

precipitation,

OP/

Belfort

(inches)

0.05/0.05

0.02/0.00

0.01/0.01

0.01/0.00

0.10/0.11

Table 1. Differences of precipitation measurements between the OTT PLUVIO 

Precipitation Gage and Belfort Universal Precipitation Gage 5-780, collected during phase 

III supplemental data evaluation

[Abbreviations: OP, OTT PLUVIO Precipitation Gage; Belfort, Belfort Universal Precipitation Gage 5-780.]

0.32/0.32

0.29/0.28

0.11/0.10

0.06/0.05

0.24/0.25

Adjusted

mean

precipitation,

OP/

Belfort

(inches)

IL11

East

IL11

West

MN16

NV03

PA15

Site

14/15

7/15

7/21

11/12

0/28

Number

of days

of lost

data

OP/

Belfort

66

109

106

56

75

Number

of precipitation

events

16.97/16.46

19.23/18.10

7.88/7.49

1.58/1.13

17.75/18.41

Total

precipitation,

OP/

Belfort

(inches)

17

51

33

34

2

Number

of false

positives

removed

52

65

73

22

73

Adjusted

number

of

events

0.10/0.11

0.06/0.06

0.03/0.03

0.02/0.03

0.13/0.12

Adjusted

median

precipitation,

OP/

Belfort

(inches)

16.78/16.46

18.53/18.10

7.72/7.49

1.24/1.13

17.73/18.41

Adjusted

total

precipitation,

OP/

Belfort

(inches)

Precipitation events dataset False positives removed dataset

IL11

East

IL11

NV03

Table 2. Differences of measurements at the National Trends Network sites using the 

paired t-test and the Wilcoxon signed-rank test during phase III supplemental data 

evaluation

Precipitation event data set False positive removed Precipitation event

data set

False positives

removed

Site

0.008

0.010

0.004

0.008

-0.009

Mean

difference

0.183

0.001

0.615

~0

0.137

p-value

0.402

0.205

0.769

0.373

0.125

p-value

0.097

~0

0.001

~0

0.543

p-value

0.439

0.199

0.130

0.144

0.446

p-value

0.006

0.007

0.003

0.005

-0.009

Mean

difference

Paired t-test Wilcoxon signed-rank test

Mean

equals

zero

Do not

reject

Do not

reject

Do not

reject

Do not

reject

Do not

reject

Median

equals

zero

Do not

reject

Do not

reject

Do not

reject

Do not

reject

Do not

reject

Mean

equals

zero

Do not

reject

Do not

reject

Do not

reject

Reject

Reject

Median

equals

zero

Do not

reject

Do not

reject

Reject

Reject

Reject

MN16

PA15

West

Table 3. Differences of precipitation measurements between the Belfort Universal

Precipitation Gage 5-780, OTT PLUVIO Precipitation Gage, and the NovaLynx Model

260-2510 Standard Rain and Snow Gage, using the paired t-test and Wilcoxon signedrank test at sites IL11, for 63 comparisons and PA15 for 64 comparisons.

[Abbreviations: --, no data; Belfort, Belfort Universal Precipitation Gage 5-780; OP, OTT PLUVIO 

precipitation gage; NovaLynx, NovaLynx Model 260-2510 Standard Rain and Snow Gage.]

0.28

0.33

0.33

0.32

0.37

0.38

0.38

Mean

precipitation

(inches)

0.06

0.07

0.11

0.08

0.19

0.20

0.20

Median

precipitation

(inches)

17.33

20.93

20.58

19.66

23.94

24.49

24.69

Total

precipitation

(inches)

Paired t-test Wilcoxon signedrank test

~0

~0

0.002

--

0.026

0.661

--

p-value

~0

0.112

0.078

--

0.003

0.203

--

p-value

Reject

Reject

Reject

--

Reject

Do not

reject

--

Mean

difference

equals

zero

0.037

0.305

-0.015

--

-0.011

-0.003

--

Mean

difference

Gage

and

site

Belfort,

IL11

OP,

IL11 East

OP,

IL11 West

NovaLynx,

IL11

Belfort,

PA15

OP,

PA15

NovaLynx,

PA15

Reject

--

Do not

reject

--

Median

difference

equals

zero

Do not

reject

Do not

reject

Reject

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 077-03

September 2003
The box plots in figure 1 show the differences in inches between 

the daily precipitation measured by the Belfort and OP precipitation 

gages. The median lines for the five sites are located at or close to 

zero, with slight variability of distribution for the middle 50 percent 

of the data. IL11 West and PA15 sites showed the greatest variability 

with the presence of several outliers. The site at PA15 had more outliers for positive differences indicating the Belfort gage recorded 

higher measurements than the OP gage.

Cumulative precipitation for all sites is shown in figure 2. 

Throughout phase III supplemental testing, the precipitation events 

measured by the OP gages were generally higher than the Belfort 

gages. The gages at PA15 were the exception; cumulative precipitation at the Belfort gage was 0.68-in. higher than the OP gage. Paired 

t-tests showed no significant differences between the gage measurements at sites IL11 East, MN16, and PA15. When the false positives 

were removed, the measurements at all sites were not significantly 

different. Wilcoxon signed-rank tests showed that only the measurements at IL11 East and PA15 were not significantly different. When 

the false positives were removed, the analysis showed no significant 

difference between measurements at all sites. 

As part of the phase III supplemental testing analysis, precipitation 

measurements obtained at sites IL11 and PA15 by the Belfort and OP 

gages were compared to precipitation measurements recorded by the 

NovaLynx gages (table 3). No data sets were removed for these comparisons. 

Cumulative precipitation measured at site IL11 for the Belfort 

gage was 17.33 in., the East OP gage was 20.93 in., the West OP 

gage was 20.58 in., and the NovaLynx gage measured 19.66 in. for 

63 comparisons (fig. 3). Paired t-tests showed significant differences 

between the OP, Belfort, and NovaLynx gage measurements. 

Wilcoxon signed-rank tests showed no significant differences 

between the NovaLynx gage and both East and West OP gage measurements; however, the NovaLynx and the Belfort gage measurements were significantly different. 

Cumulative precipitation measured at site PA15 for the Belfort 

gage was 23.94 in., the OP gage was 24.49 in., and the NovaLynx 

gage was 24.69 in. for 64 comparisons (fig. 3). Paired t-tests showed 

no significant difference between NovaLynx and OP gage measurements. Paired t-tests for the NovaLynx and the Belfort gage measurements were significantly different. The Wilcoxon signed-rank test 

showed no significant differences between the NovaLynx and OP 

gage measurements, but was significantly different for the NovaLynx 

and the Belfort gage measurements.

—Mary L. Tumbusch

References

National Atmospheric Deposition Program, 2003. NADP Site overview page, accessed March, 10, 2003 at URL

http://nadp.sws.uiuc.edu/nadpoverview.asp.

Tumbusch, M.L., 2003, Evaluation of OTT PLUVIO Precipitation 

Gage versus Belfort Universal Precipitation Gage 5-780 for the 

National Atmospheric Deposition Program: U.S. Geological 

Survey Water-Resources Investigations Report 03-4167, 25 p. 

http://pubs.water.usgs.gov/wri034167. 

0

2

4

6

8

10

12

14

16

18

20

2002

IL11 East Belfort (16.46 in.)

IL11 East OP (16.78 in.)

IL11 West Belfort (18.10 in.)

IL11 West OP (18.53 in.)

MN16 Belfort (7.49 in.)

MN16 OP (7.72 in.)

NV03 Belfort (1.13 in.)

NV03 OP (1.24 in.)

PA15 Belfort (18.41 in.)

PA15 OP (17.73 in.)

Figure 2. Cumulative precipitation measurements from the Belfort Universal

Precipitation Gage 5-780 and OTT PLUVIO precipitation gages.

Jan 15 Jan 29 Feb 12 Feb 26 Mar 12 Mar 26 Apr 9 Apr 23 May 7 May 21 June 4 June 18 July 2

CUMULATIVE PRECIPITATION, IN INCHES

0

5

10

15

20

25

30

Jan 15 Jan 29 Feb 12 Feb 26 Mar 12 Mar 26 Apr 9 Apr 23 May 7 May 21 June 4 June 18 July 2 July 16

2002

IL11 Stick (19.66 in)

IL11 Belfort (17.33 in)

IL11 West OP (20.58 in)

IL11 East OP (20.93 in)

PA15 Stick (24.69 in)

PA15 Belfort (23.94 in)

PA15 OP (24.49 in)

Figure 3. Cumulative precipitation measurements from the Belfort Universal

Precipitation Gage 5-780, OTT PLUVIO precipitation gage, and NovaLynx Model

260-2510 Standard Rain and Snow Gage for the sites at IL11 East, IL11 West, 

and PA15. CUMULATIVE PRECIPITATION, IN INCHES Illinois State Water Survey

2204 Griffith Dr.

Champaign, IL 61820-7495

Tel: (217) 244-5459

Fax: (217) 333-4983

URL: http://nadp.sws.uiuc.edu

Public Information Assistant

U.S. Geological Survey

333 West Nye Lane, Room 203

Carson City, NV 89706-0866

Tel: (775) 887-7649

Fax: (775) 887-7629

Email: GS-W-NVpublic-info@usgs.gov

URL: http://nevada.usgs.gov

 For information on water resources in Nevada and other USGS Programs:

For additional information related to NADP contact:

September 2003 USGS Fact Sheet 077-03

Largest value less than or equal

to the 75th percentile plus

1.5 times interquartile range

Smallest value less than or equal

to the 25th percentile minus

1.5 times interquartile range

Remaining one percent of the data

not inclusive in the distribution tails

3rd quartile

Median

1st quartile

IL ll East IL ll West MN 16 NV 03 PA 15

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

SITE ID

DIFFERENCES, IN INCHES, BELFORT-OP Figure 1. Differences between the daily precipitation measured by the Belfort 

Universal Precipitation Gage 5-780 and OTT PLUVIO precipitation gages.