reflectance

Time Domain Reflectometry at the Sevilleta National Wildlife Refuge, New Mexico (1996-2005)

Abstract: 

This file contains hourly time-domain reflectometry (TDR) soil moisture data for 1996-2005. A key factor in a spatially explicit water-balance model is a measure of moisture in the soils over time. This metric is crucial for both calibration and validation of such a model. One of the best methods of measuring soil moisture on a continuous basis is TDR. Therefore, a network of TDR soil moisture sensors was installed at all meteorological stations on the Sevilleta National Wildlife Refuge. At two of the sites the sensors were measured on an hourly basis in conjunction with the meteorological variables. At the four other sites the sensors were measured on a much less frequent basis - about every two weeks. Sensors were installed in pits in sets of five. One sensor was installed vertically adjacent to the pit to measure the top 30 cm of soil. The other four were installed horizontally in the face of the pit at 5, 10, 20, and 40 cm. Pits were then backfilled.

Core Areas: 

Additional Project roles: 

86

Data set ID: 

78

Keywords: 

Purpose: 

To measure moisture in soils at the field site over time.

Data sources: 

sev078_tdr_12092011.txt

Methods: 

Analytical Procedures:

Probes were measured every hour and collected propogating velocities were converted to soil moisture values using the Ledieu calibration. Each probe was run in sequence and the 15 probes could take 4 or 5 minutes to read.

Sampling Design:

Three sites were designated as water-balance monitoring sites: 1.) Deep Well - Met 40, 2.) Rio Salado - Met 44 and 3.) Field Station Sta1. At these sites replicate TDR probes were installed at specific depths while other probes were installed vertically to get an average soil moisture for the top 30 cm of soil.

Measurement Techniques: Time Domain Reflectometry:

TDR measures the reflectance of an electromagnetic pulse down a probe. This reflectance is affected by the amount of moisture in the soil surrounding the probe. Algorithms have been developed relating reflectance to volumetric soil moisture that work for most soils. The Campbell system has a built in program which reads the inflection points of the wave-form and automatically outputs soil moisture.

Locations where measurements were taken by year:

1996:1, 40, 41, 42, 43, 44, 45

1997:1, 40, 41, 42, 43, 44, 45

1998:1, 40, 41, 42, 43, 44, 45

1999:40,44,1

2000:40,42

2001:40,42

2002:40

2003:40

2004:40

2005:40

Instrumentation: 

Instrumentation: CR10 Datalogger; Tecktronx 1502B Cable Tester; Multiplexer SDMX50; TDR probe 30 cm

Instrument Name: Soil Moisture Potential Probe Manufacturer: Campbell Scientific Model Number: 227

Maintenance: 

2/19/1996 - Douglas Moore:

Jan 12, 1996 Sta 40 Installed probes in two more pits. Reprogrammed so data is being collected from all 15 probes.

Jan 19, 1996 Sta 01 Installed probes in two more pits.

Jan 19, 1996 Sta 44 Replaced probe w3_30 which had been chewed off by rodent.

Jan 30, 1996 Sta 41 Installed probes in Pit 1.

Feb 07, 1996 Sta 45 Installed probes in two more pits.

Feb 09, 1996 Sta 01 Installed datalogger, TDR enclosure and multiplexer. Installed program to collect data.

Feb 14, 1996 Sta 01 Replaced w1_10 probe. Changed program so battery voltage is collected.

Feb 23, 1996 Sta 42 Installed probes in two more pits.

Feb 28, 1996 Sta 40 Began having problems with data - missing hours or getting -699 due to dying internal battery in reflectometer.

Mar 08, 1996 Sta 40 Pulled reflectometer out to send back to Campbell.

Mar 12, 1996 Sta 01 Pulled reflectometer out to put in at Sta 40.

Mar 12, 1996 Sta 40 Put reflectometer from Sta 1 into Sta 40.

Mar 20, 1996 Sta 43 Installed probes in two pits (except w2_30).

Mar 27, 1996 Sta 41 Installed probes in a second pit.

Apr 01, 1996 Sta 41 Replaced faulty w2_30 probe.

Apr 08, 1996 Sta 43 Installed w2_30 probe.

12/15/1998: Douglas Moore:

 Jan 22, 1997 Sta 44 Replaced TDR meter with one from field station.

Jan 22-April 04, 1997 Sta 40 W1_5 bad data replaced with- 999.

Apr 16, 1997 Sta 40 New w2_5 - 5 cm probe in pit B.

Apr 30-May 07, 1997 Sta 01 Missing data - Lost power to datalogger.

May 14-May 21, 1997 Sta 01 Missing data - Forgot to turn reflectometer on after returning to shelter.

Aug 01-Aug 20, 1997-Sta 40 w2_30 data bad changed to -999.

Aug 20, 1997 Sta 40 Replaced w2_30 sensor.

Quality Assurance: 

This data was QA'd/QC'd.

Additional information: 

Personnel associated with the Data Collection / Data Processing: Karen Wetherill, Yang Xia, Terri Koontz, Amaris Swann, Michell Thomey, Jay McLeod, Jim Elliott, Chelsea Crenshaw

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