soil sampling
Processing soil samples during SGP97

Gravimetric soil moisture sampling


The Data
The Files
Formats
Name and Directory Information
The Science
Sampling Plan
Procedures
Data Processing
Data Access and Contacts
FTP Site
Points of Contact

Raw Data Summary backSoil Moisture page

The Data

The results obtained in the surface gravimetric soil moisture (GSM) sampling are provided. Soil moisture is gravimetric, not volumetric. For interpretation of the codes used for areas and sites please refer to the experiment plan. Field notebooks are available for use at the USDA Hydrology Lab, they will not be loaned out. Also included in this information file is the background material from the sampling plan describing the design and protocols used.

The Files

Two data files will be available, the summary (means and standard deviations of all fields and days) and the raw data for each field on each day. Files are all ASCII text.

Formats

Raw Data
FormatASCII text table
Column HeadingsArea ID
Site ID
Can ID
Date (Year-Month-Day)
Day of Year
Wet Weight
Dry Weight
GSM
Note (if any)
Summary
FormatASCII text table
Column HeadingsArea ID
Site ID
Date (Month-Day-Year)
Day of Year
Mean GSM
Standard Deviation of GSM
Note (if any)

Name and Directory Information

File Naming Convention

  • Raw Data File (LIMITED DISTRIBUTION) gsmraw.txt
  • Summary File gsmsum.txt

Directory path

The directory path to the Gravimetric Soil Moisture ftp site is

ftp://disc1.sci.gsfc.nasa.gov/data/sgp97/grnd_based_soil_moisture/gsmsum.txt

The Science

Sampling Plan

For the most part, sampling was performed on sites approximately a quarter section (0.8 km by 0.8 km) in size. Attempts were made to sample several adjacent sites that could be clustered. In addition, some sites were sampled solely for surface-profile correlations and consist of the area immediately surrounding a profile location.

Sites with "Full" sampling generally involved two transects separated by 400 m with a sample every 100 m resulting in 14 samples per site. Profile only sites consisted of 9 samples collected over a 20 m by 20 m grid near the profile location. A standardized tool was used to extract a sample of the 0-5 cm soil layer. Sample location was not critical in this approach. The grid was used only as an aid in stratifying the distribution of samples. In fields that were being used for surface variability studies, an attempt was made to sample near the markers.

Procedures

The Gravimetric Soil Moisture (GSM) samples were collected from all sites on a daily basis. After the retrieval of all samples they were weighed in their wet' state and put in the oven. The next day, approximately 22 hours later, the oven-dry samples were weighed again. To speed up weighing and to reduce the data processing, the process was partially automated by connecting the balances with PC's.

Sampling Protocol The gravimetric soil moisture (GSM) sampling was intended to estimate the site average and standard deviation. Precise location within the site was not important, however, the samples were spatially distributed to obtain meaningful statistics. For this reason a grid was used. Two types of sampling designs were employed, Full and Profile. The actual soil moisture sampling method was the same but the distribution and number of samples was different.

Wet Weight Procedure

  1. The balance will be connected to a computer that will record the weight.
  2. Turn on computer and get the program running. There will be an instruction sheet available on site and instruction will be provided.
  3. Process your samples on a site basis and in sample numeric order.
  4. Place the open cans (the lid goes on the bottom of the can) in the drying oven. Arrange them sequentially.
  5. There will be sheets available for manually recording the weights if you encounter unresolvable problems with the computer operation.

Dry Weight Procedure

  1. All samples should remain in the oven for approximately 20-22 hours at 105oCThere will be a raw data file for each site on each day.
  2. Try to remove samples in the order they were put in. This should result in sequential groups for sites. Only remove a few sites at a time and keep oven running.
  3. These samples will be hot. Wear the gloves provided.
  4. Follow the instructions provided for the software to enter the dry weight of can (with its lid).
  5. Dump the soil after verifying data and clean the can with the brush provided.
  6. Repack the can boxes, check that can numbers are readable and replace any damaged or lost cans with spares.

Data Processing

  1. There is a raw data file for each site on each day.
  2. There is a summary file for each day for each area that will contain the means and standard deviations.
  3. All files are backed up with a floppy disk copy.
  4. The summary file was transmitted to a central collection point on a daily basis.

Data Access and Contacts

FTP Site

The Gravimetric Soil Moisture Summary File from SGP97 is in the following GES DISC ftp site:

FTP iconSummary file (ASCII)

The Gravimetric Soil Moisture raw data files from SGP97 are for limited distribution only. To obtain them, contact Principal Investigator Thomas Jackson at the Agricultural Research Service Hydrology Lab (see "Points of Contact below.")

Points of Contact

The Principal Investigator for the SGP97 Gravimetric Soil Moisture data is

Thomas J. Jackson
USDA ARS Hydrology Lab
Bldg. 007, Rm. 104, BARC-West
Beltsville, MD 20705

tjackson@hydrolab.arsusda.gov
301-504-8511 (voice)

For more information using the SGP97 GES DISC data, contact:

Hydrology Data Support Team
Goddard Earth Sciences
Data and Information Services Center (GES DISC)
Code 610.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771

hydrology-disc@listserv.gsfc.nasa.gov
Voice: 301-614-5165
Fax: 301-614-5268

Soil moisture page
Last update:Thu Jan 28 09:34:12 EST 1999
Page Info: Hydrology Data Support Team -- hydrology-disc@listserv.gsfc.nasa.gov
Web Curator: Anthony Drake
NASA official: Steve Kempler, DAAC Manager -- Steven.J.Kempler@nasa.gov