Measurements were made at six stations on Indian grass, switch grass, Big bluestem, little bluestem, and tall dropseed. Leaf water potential measurements were usually made on the same leaf that optical measurements were made and on leaves of surrounding plants. Measurements were made on the most recently expanded leaf of the selected plant unless specified. Measurements were also made of older green and yellow leaves on a plant. Leaf water potential measurements can be linked with the leaf optical properties data if the plant number in both sets of data are known.
Plant water potential values measured just before dawn will provide the highest plant water potential (smallest negative value) during the day and also provides a reasonable estimate of the soil water potential. It is hypothesized that as the leaf water potential decreases (large negative value) that there may be some change in the internal structure of the leaf that would be detectable in one or more of the Nebraska Multiband Leaf Radiometer (NMLR - instrument used during leaf optical measurements) wavebands. It is also hypothesized that the amounts of water in a leaf will be lowest at low water potential and that this might also be detectable with the NMLR especially in the mid-IR wavebands.
The Total Leaf Tissue Water Potential Data Set was collected from June 1 through August 12 1988, and from June 14 through August 12, 1989. The objective of this study was to determine the influence of plant water status on surface reflectance factors. Measurements were made at six stations in the FIFE study area. Measurements were made on Indian grass, Switch grass, Big bluestem, little bluestem, and tall dropseed.
The objective was to determine the influence of plant water status on surface reflectance factors.
Total leaf tissue water potential.
1988: Measurements were made at three stations: 10 (sitegrid = 3414-PBB), 811 (sitegrid = 4439-PBB), and 31 (sitegrid = 2139-PBB). Measurements were made on the most recently expanded leaf of the selected plant unless specified. Measurements were also made of older green and yellow leaves on a plant. Measurements were made on Indian grass, Switch grass and Big bluestem. Measurements were usually coordinated with leaf optical measurements (i.e., leaf water potential measurements were made on the same leaf that optical measurements were made and on leaves of surrounding plants. Occasionally predawn measurements were made. Leaf water potential measurements can be linked with the leaf optical properties data if the plant number in both sets of data are known.
1989: Measurements were made at three stations: 906 (sitegrid = 2133-PBB), 916 (sitegrid = 4439-PBB) and 966 (sitegrid = 2437-PBB). Measurements were made on Big bluestem, Indian grass, and Switch grass at all three sites. Little bluestem was measured at site 916 (sitegrid = 4439-PBB) and tall dropseed was measured at site 906 (sitegrid = 2133-PBB).
Blaine L. Blad, Professor and Head
Elizabeth A. Walter-Shea, Asst. Professor
University of Nebraska
Measuring and Modeling Near-Surface Reflected and Emitted Radiation Fluxes at the FIFE study area.
Cynthia J. Hays
Mark A. Mesarch
Elizabeth A. Walter-Shea
The Total Leaf Tissue Water Potential data were collected by B.L. Blad, E.A. Walter-Shea, C.J. Hays, and M.A. Mesarch of the University of Nebraska.
Since transpiration rates at night are small or near zero the water potential inside the plant comes into equilibrium with the water potential of the soil in the root zone. Therefore plant water potential values measured just before dawn will provide the highest plant water potential (i.e., smallest negative value) during the day and will also provide a reasonable estimate of the soil water potential. It is hypothesized that as the leaf water potential decreases (i.e., large negative value) that there may be some change in the internal structure of the leaf that would be detectable in one or more of the Nebraska Multiband Leaf Radiometer (NMLR - instrument used during leaf optical measurements) wavebands.
It is also hypothesized that the amounts of water in a leaf will be lowest at low water potential and that this might also be detectable with the NMLR especially in the mid-IR wavebands.
A pressure chamber manufactured by Precision Machine, Inc. Lincoln, NE connected to a tank of compressed nitrogen was used for this study. A slitted gasket was used for sealing the leaf blade in the chamber.
The aim was to measure leaf water potential.
Total leaf tissue water potential.
A leaf is excised from the plant and placed in the chamber with a small portion of the cut end of the leaf protruding through the seal. Pressure is applied to the tissue until an endpoint is reached at which water just appears at the cut end of the leaf blade. When water appears, the pressure applied to the tissue is equal to the negative of the leaf water potential (Campbell 1990).
Precision Machine, Inc.
2933 N. 36th St.
Lincoln, NE 68504
The leaf blade was inserted into a humidified plastic bag, to prevent water loss from the leaf blade and a rise in leaf temperature during the measurement period. The leaf was then cut from the plant using a razor blade and placed in the pressure chamber with a small portion of the cut end of the leaf blade protruding through the seal. Pressure was then applied until an endpoint was reached, when water appeared at the cut end of the leaf blade. The endpoint pressure was recorded. A magnifying glass was used to facilitate seeing the water. The procedure was repeated to obtain a second end point pressure measurement.
The two measurements were made to ensure that the rate of pressure increase was slow enough to give the water in the leaf time for equilibration. If the second measurement is lower than the first the rate of pressure increase was probably too high (Campbell 1990). The two measurements should be approximately the same (+/-1.033 bar).
The FIFE study area, with area extent of 15 km by 15 km, is located south of the Tuttle Reservoir and Kansas River, and about 10 km from Manhattan, Kansas, USA. The northwest corner of the area has UTM coordinates of 4,334,000 Northing and 705,000 Easting in UTM Zone 14.
Data samples were collected and measurements were made at several sites of the FIFE study area. Representative areas of the site were sampled. Species were selected to be representative of the site. Below is a list of FIFE sites from which data were collected:
SITEGRID STN NORTHING EASTING LATITUDE LONGITUDE ELEV -------- --- -------- ------- -------- --------- ---- 2133-PBB 906 4329726 711604 39 05 34 -96 33 12 443 2437-PBB 966 4329150 712375 39 05 15 -96 32 41 3317-PBB 810 4327463 708463 39 04 24 -96 35 25 420 4139-PBB 831 4325850 712780 39 03 28 -96 32 27 385 4439-PBB 916 4325193 712773 39 03 06 -96 32 28 443 4439-PBB 811 4325219 712795 39 03 07 -96 32 27 445 SITEGRID SLOPE ASPECT -------- ----- ------ 2133-PBB 1 TOP 2437-PBB 3317-PBB 13 W 4139-PBB 3 W 4439-PBB 2 N 4439-PBB 2 N
These are point data.
Measurements were made from June 1 through August 12 1988, and from June 14 through August 12, 1989. The measurement time ranged from 1011 to 2409 GMT. Measurements were not made continuously.
The specific dates of data collection were:
01-JUN-88 14-JUN-89 04-AUG-89 02-JUN-88 11-JUL-89 05-AUG-89 29-JUN-88 13-JUL-89 06-AUG-89 30-JUN-88 26-JUL-89 07-AUG-89 06-JUL-88 27-JUL-89 08-AUG-89 14-JUL-88 28-JUL-89 10-AUG-89 09-AUG-88 29-JUL-89 12-AUG-89 10-AUG-88 01-AUG-89 12-AUG-88 02-AUG-89
Measurements were made throughout a day. Measurements of one leaf required 1 to 4 minutes. The optimum time interval from one leaf to the next was generally about 2 to 3 minutes during a measurement period.
The SQL definition for this table is found in the LEAF_H20.TDF file located on FIFE CD-ROM Volume 1.
Parameter/Variable Description Range Units Source
SITEGRID_ID This is a FIS grid location code. FIS Site grid codes (SSEE-III) give the south (SS) and east (EE) cell number in a 100x100 array of 200m square cells. The last 3 characters (III) are an instrument identifier.
STATION_ID The station ID designating the 810, FIS location of the observations. 811, 831, 906, 916, 966
OBS_DATE The date of the observation. min = 01-JUN-88, FIS max = 12-AUG-89
OBS_TIME The time the observation was min = 1011, [GMT] FIS taken, which is after the leaf was max = 2409 cut (see CUT_TIME).
OBS_SECONDS The seconds part of the OBS_TIME. min = 0, [seconds] FIS max = 60
SPECIES_NAME The common name of the plant Big Bluestem, FIS being measured. Indian Grass, Little Bluestem, Switch Grass, Tall Dropseed
LTER_SPECIES_CODE The LTER species code (see table 2, FIS VEG_SPECIES_REF) for the species 3, of the leaf measured. 15, 18, 21
OBS_SEQUENCE This is the number of the min = 1, FIS observation sequence made on the max = 12 same leaf sample. A leaf sample is identified by the same CUT_TIME and CUT_SECONDS.
CUT_TIME The time that the leaf was cut. min = 1031, [GMT] FIS max = 2225
CUT_SECONDS The second part of the CUT_TIME. min = 1, [seconds] FIS max = 60
WATER_POTNTL The leaf water potential. This min = 0, [Mega- FIS value is actually negative, even max = 6.888 Pascals] though it is reported as positive.
FIFE_DATA_CRTFCN_CODE * The FIFE Certification Code for CPI=Checked FIS the data, in the following format: by Principal CPI (Certified by PI), CPI-??? Investigator (CPI - questionable data).
LAST_REVISION_DATE data, in the format (DD-MMM-YY). max = 18-MAR-91
Decode the FIFE_DATA_CRTFCN_CODE field as follows:
The primary certification codes are: EXM Example or Test data (not for release) PRE Preliminary (unchecked, use at your own risk) CPI Checked by Principal Investigator (reviewed for quality) CGR Checked by a group and reconciled (data comparisons and cross checks)
The certification code modifiers are: PRE-NFP Preliminary - Not for publication, at the request of investigator. CPI-MRG PAMS data which is "merged" from two separate receiving stations to eliminate transmission errors. CPI-??? Investigator thinks data item may be questionable.
SITEGRID_ID STATION_ID OBS_DATE OBS_TIME OBS_SECONDS SPECIES_NAME ----------- ---------- --------- -------- ----------- ------------- 2437-PBB 966 14-JUN-89 1534 19 BIG BLUESTEM 2437-PBB 966 14-JUN-89 1534 54 BIG BLUESTEM 2437-PBB 966 14-JUN-89 1538 16 BIG BLUESTEM 2437-PBB 966 14-JUN-89 1538 34 BIG BLUESTEM LTER_SPECIES_CODE OBS_SEQUENCE CUT_TIME CUT_SECONDS WATER_POTNTL ----------------- ------------ -------- ----------- ------------ 2 1 1532 59 .5170 2 2 1532 59 .7240 2 3 1537 6 .5520 2 4 1537 6 .5860 FIFE_DATA_CRTFCN_CODE LAST_REVISION_DATE --------------------- ------------------ CPI 18-MAR-91 CPI 18-MAR-91 CPI 18-MAR-91 CPI 18-MAR-91
This data set contains point data. Measurements were made from June 1 through August 12 1988, and from June 14 through August 12, 1989. Measurements were not made continuously.
A general description of data granularity as it applies to the IMS appears in the EOSDIS Glossary.
The CD-ROM file format consists of numerical and character fields of varying length separated by commas. The character fields are enclosed with a single apostrophe. There are no spaces between the fields. Each file begins with five header records. Header records contain the following information: Record 1 Name of this file, its table name, number of records in this file, path and name of the document that describes the data in this file, and name of principal investigator for these data. Record 2 Path and filename of the previous data set, and path and filename of the next data set. (Path and filenames for files that contain another set of data taken at the same site on the same day.) Record 3 Path and filename of the previous site, and path and filename of the next site. (Path and filenames for files of the same data set taken on the same day for the previous and next sites (sequentially numbered by SITEGRID_ID)). Record 4 Path and filename of the previous date, and path and filename of the next date. (Path and filenames for files of the same data set taken at the same site for the previous and next date.) Record 5 Column names for the data within the file, delimited by commas. Record 6 Data records begin.
Each field represents one of the attributes listed in the chart in the Data Characteristics Section and described in detail in the TDF file. These fields are in the same order as in the chart.
PAVG = P((1) + P(2)Ù)/2 [Eq.1]
P(1 or 2) = endpoint pressure reading (psi)
PAVG = average endpoint pressure reading (psi)
WATERPOT = -0.0068948 * PAVG [Eq.2]
PAVG = average endpoint pressure reading (psi)
WATERPOT = total leaf water potential (MPa)
If the difference between the two endpoint pressure readings were greater than 1.033 bars (15 psi) the data were discarded (see the Data Acquisition Methods Section).
Equation 1 is used to calculate the average endpoint pressure reading from the chamber. Equation 2 is used to convert psi to MPa and to calculate the total leaf water potential. The total leaf water potential is equal to the negative of the applied pressure at the endpoint (Campbell 1990).
Errors can result if the leaf sample: 1) is allowed to lose moisture, 2) temperature is allowed to rise in the chamber, or 3) is not tightly sealed by the chamber gasket (Hsiao 1990).
Sometimes it is difficult to detect the exact time and pressure when water first exudes from the leaf as the wetting can be subtle. This will cause leaf water potentials to be slightly lower than they actually are.
The rate of pressure increase in the chamber must be slow enough to give the water in the leaf time for equilibration. If the pressure is increased too rapidly the pressure reading will be too high (Campbell 1990). Water loss from the leaf and temperature increase of leaf and chamber should be kept to a minimum for an accurate measurement.
Data were validated by looking for consistency of readings of different leaves taken during a given measurement period. If leaf water potential values were too low then an additional leaf was selected for measurement and any seemingly erroneous data were omitted.
Data are also validated by the repeated readings on a single leaf. If leaf water potential values differed more than 15 psi the data were omitted and an additional leaf was selected.
It is very difficult (if not impossible) to determine the precision and accuracy of plant water potential measurements. Readings on the same leaf are generally repeatable to one bar or less.
No quantitative assessment was made, see the Confidence Level/Accuracy Judgment .
FIS staff applied a general Quality Assessment (QA) procedure to the data to identify inconsistencies and problems for potential users. As a general procedure, the FIS QA consisted of examining the maximum, minimum, average, and standard deviation for each numerical field in the data table. An attempt was made to find an explanation for unexpected high or low values, values outside of the normal physical range for a variable, or standard deviations that appeared inconsistent with the mean. In some cases, histograms were examined to determine whether outliers were consistent with the shape of the data distribution.
The discrepancies, which were identified, are reported as problems in the Known Problems with the Data Section.
The data verification performed by the ORNL DAAC deals with the quality of the data format, media, and readability. The ORNL DAAC does not make an assessment of the quality of the data itself except during the course of performing other QA procedures as described below.
The FIFE data were transferred to the ORNL DAAC via CD-ROM. These CD-ROMs are distributed by the ORNL DAAC unmodified as a set or in individual volumes, as requested. In addition, the DAAC has incorporated each of the 98 FIFE tabular datasets from the CD-ROMs into its online data holdings. Incorporation of these data involved the following steps:
Each distinct type of data (i.e. "data set" on the CD-ROM), is accompanied by a documentation file (i.e., .doc file) and a data format/structure definition file (i.e., .tdf file). The data format files on the CD-ROM are Oracle SQL commands (e.g., "create table") that can be used to set up a relational database table structure. This file provides column/variable names, character/numeric type, length, and format, and labels/comments. These SQL commands were converted to SAS code and were used to create SAS data sets and subsequently to input data files directly from the CD-ROM into a SAS dataset. During this process, file names and directory paths were captured and metadata was extracted to the extent possible electronically. No files were found to be corrupted or unreadable during the conversion process.
Additional Quality Assurance procedures were performed as follows:
As errors are discovered in the online tabular data by investigators, users, or DAAC staff, corrections are made in cooperation with the principal investigators. These corrections are then distributed to users. CD-ROM data are corrected when re-mastering occurs for replenishment of CD-ROM stock.
While potential is negative in value, the data in this data set is reported as positive values because they have been multiplied by a negative constant.
To be able to link leaf water potential data with the leaf optical data one needs to know the plant number in both data sets.
This data could be used in conjunction with other data measured using the following instruments:
This data set can be utilized to determine the influence of plant water status on surface reflectance factors. Leaf water potential measurements can be linked with the leaf optical properties data if the plant number in both sets of data are known.
The FIFE field campaigns were held in 1987 and 1989 and there are no plans for new data collection. Field work continues near the FIFE site at the Long-Term Ecological Research (LTER) Network Konza research site (i.e., LTER continues to monitor the site). The FIFE investigators are continuing to analyze and model the FIFE data from the field campaigns to produce new data products.
Software to access the data set is available on the all volumes of the FIFE CD-ROM set. For a detailed description of the available software see the Software Description Document.
ORNL DAAC User Services
Oak Ridge National Laboratory
Telephone: (865) 241-3952
FAX: (865) 574-4665
ORNL Distributed Active Archive Center
Oak Ridge National Laboratory
Telephone: (865) 241-3952
FAX: (865) 574-4665
Users may place requests by telephone, electronic mail, or FAX. Data is also available via the World Wide Web at http://daac.ornl.gov.
The Total Leaf Tissue Water Potential data are available on FIFE CD-ROM Volume 1. The CD-ROM filename is as follows:
Where xxxx is the four digit code for the location within the FIFE site grid. Note: capital letters indicate fixed values that appear on the CD-ROM exactly as shown here, lower case indicates characters (values) that change for each path and file.
The format used for the filenames is: ydddgrid.sfx, where grid is the four-number code for the location within the FIFE site grid, y is the last digit of the year (e.g. 7 = 1987, and 9 = 1989), and ddd is the day of the year (e.g., 061 = sixty-first day in the year). The filename extension (.sfx), identifies the data set content for the file (see the Data Characteristics Section) and is equal to .LWP for this data set.
Campbell, G.S. 1990. Instrumentation of studying vegetation canopies for remote-sensing in optical and thermal infrared regions - water potential in soils and plants. Remote Sensing Reviews. 5:249-261.
Hsiao, T.C. 1990. Measurements of Plant Water Status. In Stewart, B.A. and D.R. Nielson (eds.). Irrigation of Agricultural Crops. Agronomy Monograph. 30:244-279.
Contact the EOS Distributed Active Archive Center (DAAC) at Oak Ridge National Laboratory (ORNL), Oak Ridge, Tennessee (see the Data Center Identification Section). Documentation about using the archive and/or online access to the data at the ORNL DAAC is not available at this revision.
A general glossary for the DAAC is located at Glossary.
A general list of acronyms for the DAAC is available at Acronyms.
May 4, 1994 (citation revised on October 14, 2002).
Warning: This document has not been checked for technical or editorial accuracy by the FIFE Information Scientist. There may be inconsistencies with other documents, technical or editorial errors that were inadvertently introduced when the document was compiled or references to preliminary data that were not included on the final CD-ROM.
Previous versions of this document have been reviewed by the Principal Investigator, the person who transmitted the data to FIS, a FIS staff member, or a FIFE scientist generally familiar with the data.
Blad, B. L., and E. A. Walter-Shea. 1994. Total Leaf Tissue Water Potential (FIFE). Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/126. Also published in D. E. Strebel, D. R. Landis, K. F. Huemmrich, and B. W. Meeson (eds.), Collected Data of the First ISLSCP Field Experiment, Vol. 1: Surface Observations and Non-Image Data Sets. CD-ROM. National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland, U.S.A. (available from http://www.daac.ornl.gov).