The results showed that estimated values of net CO2 flux varied between about 0.25 and 1.0 [mg][m^-2][sec^-1] during IFC-2 and IFC-3, and around zero during IFC-4. Resistances ranged from 80 [sec][m^-1] to 300 [sec] [m^-1] during IFC-2 and IFC-3, rising to very high values (greater than 1000 [sec][m^-1]) during IFC-4.
The Canopy Photosynthesis Data Set data were collected from five sites within the FIFE study area during July 1, 1987 through October 12, 1987. The data set contains estimates of canopy photosynthetic rates, respiration rates, and bulk stomatal resistance.
The objectives were to estimate canopy photosynthetic rates, respiration rates, and bulk stomatal resistance using sealed Plexiglas chambers.
Vapor pressure, air temperature, surface temperature, incident photosynthetically active radiation, rate of photosynthesis, and total canopy resistance.
Measurements of photosynthetic respiration and bulk stomatal resistance of the plant canopy were made using a Plexiglas chamber equipped with a LI-COR CO2 gas analyzer. Measurements of incident Photosynthetically Active Radiation (PAR) were made throughout the day within and outside the chamber. These data were collected from sites 60 (2133-PSB), 16 (4439-PSB), 28 (6943-PSB), 36 (2655-PSB), and 44 (2043-PSB) during July 1, 1987 through October 12, 1987, which fell within FIFE IFCs 1-4. Three sites (2133-PSB, 4439-PSB and 2043-PSB) were located within the northwest quadrant of the FIFE study area. The other sites were distributed within the rest of the FIFE area.
The results showed that estimated values of net CO2 flux varied between about 0.25 and 1.0 [mg][m^-2][sec^-1] during IFC-2 and IFC-3, and around zero during IFC-4. Resistances ranged from 80 [sec][m^-1] to 300 [sec] [m^-1] during IFC-2 and IFC-3, rising to very high values (greater than 1000 [sec][m^-1]) during IFC-4. The FIFE Interim Report (Sellers et al., 1990) shows some results for individual sites.
Dr. G. Asrar
Dr. P.J. Sellers
NASA Goddard Space Flight Center
Canopy Photosynthesis and Resistance Chamber Measurements During FIFE.
Dr. P.J. Sellers
NASA Goddard Sp. Fl. Ctr.
Dr. G. Asrar
The Canopy Photosynthesis data were collected by G. Asrar of NASA Headquarters and P.J. Sellers of NASA Goddard Space Flight Center.
Photosynthesis is measured by monitoring the net exchange of CO2 from the canopy to the atmosphere while the canopy is enclosed in a chamber. The rate at which the CO2 concentration changes within the chamber over intervals of 10 - 20 seconds is measured. The net photosynthesis rate is then calculated using this rate of change and other factors, such as the amount of canopy area enclosed, the volume of the enclosure, and temperature (Farquhar et al., 1982).
Stomatal conductance is measured by monitoring the humidity within an enclosed chamber, which normally rises as the leaves transpire. The increase in humidity is balanced by the flow of partially dried air returning to the chamber from the CO2 analyzer. The transpiration rate is calculated from the change in canopy chamber humidity with time (if any) and the flow rate of that portion of the total flow, which passes through the desiccant. The transpiration rate is then used with the leaf and air temperatures to calculate total leaf resistance, from which the boundary layer resistance is subtracted, yielding the stomatal resistance and conductance.
An airtight Plexiglas chamber of dimensions 1.8 m high, 0.8 m long, and 0.8 m wide, was equipped with a LI-COR 6200 gas analyzer, a system console, and a sensor housing containing an infrared thermometer and quantum sensor. A frame fixed to the soil surface, which forms a seal with the chamber (box) when the latter is placed over it, was built around the plants whose canopy were to be measured. The chamber was placed on these frames thus sealing the internal air for sampling.
The complete system was capable of monitoring the canopy/ground surface temperature and air temperature, CO2 concentration, and water vapor concentration at a 1-second time resolution. Five frames were placed at sites 6 (2132-PSB), 16(4439-PSB), 28 (6943-PSB), 36 (2655-PSB) and 44 (2043-PSB).
A Quantum Sensor was used for measurement of incident PAR.
The aim was to measure the canopy photosynthesis rates, respiration rates, and bulk stomatal resistance at the FIFE study area.
Photosynthetically active radiation, photosynthesis rate, air and canopy surface temperature, vapor pressure, stomatal resistance.
A portion of the plant canopy was enclosed in a fabricated chamber, which is attached to a LI-6200 gas exchange system. Gas is re-circulated between the canopy chamber and the LI-6200 console, which contains a computer to do all calculations from various sensors monitoring the operation of the system.
The chamber is placed over the plant canopy and the dry-air flow rate adjusted to maintain the chamber relative humidity at the value of the ambient air. A small amount of carbon dioxide is injected into the chamber so that the concentration does not drop significantly during this initial period. Logging on the LI-6200 is begun when the concentration of carbon dioxide is near the ambient value. As the leaves photosynthesize the carbon dioxide, and concentration in the chamber drops, it is possible to determine the canopy photosynthetic rate as a function of carbon dioxide concentration inside and outside the leaves.
After the carbon dioxide concentration in the chamber has dropped such that the canopy photosynthetic rate is about half of its initial rate, some carbon dioxide is injected into the chamber to raise the concentration to about 400 to 500 micromol per mol. Then the photosynthetic rate as a function of higher carbon dioxide concentrations is measured until the canopy photosynthetic rate returns to the original value. Matching of initial and final canopy photosynthetic rates and internal CO2 concentrations is a requirement for acceptable data because it provides some assurance that the canopy is functioning in a stable mode.
The Plexiglas chamber (box) dimensions were 1.8 m x 0.8 m x 0.8 m.
Gas Analyzer and Quantum Sensor:
4421 Superior Street
P.O. Box 4425
Lincoln, NE 68504.
Plexiglas chamber was fabricated at:
University of Maryland
College Park, MD
The gas analyzer was factory calibrated over a range of temperatures by generating data that relates C02 concentration to voltage output of the analyzer and fitting the response with a third-order polynomial. Factory calibration is for 0-1500 ppm; higher ranges are possible through user calibration. Calibration accuracy is enhanced by the use of the National Bureau of Standard traceable standard gases in the factory linearization procedure.
During FIFE, calibration of the analyzer was done by adjusting the zero and span knobs located on the analyzer housing. The minimal zero and span drift of the analyzer requires few adjustments in the field. Temperature effects are automatically compensated for in the software. The zero was checked approximately once each hour using the zero reference gas, which was generated by using the soda lime scrubber within the analyzer. The span was set by flowing a known concentration of CO2 through the analyzer.
The quantum sensor was factory calibrated.
LI-6200: Available from LI-COR, Inc.
Quantum sensor: Available from LI-COR, Inc.
LI-6200: Accuracy of photosynthetic rate 5-10%.
Accuracy of stomatal conductance 10-20%.
LI-6200 was calibrated at the beginning of each run and periodically using known concentrations of CO2 and a dry-air feed.
Recalibration was not necessary for the quantum sensor.
The Plexiglas chamber (box) was placed over the fixed frame surrounding the plants, whose canopy were to be measured, for a few minutes at a time. Carbon dioxide and water vapor exchange between the plant canopy and the air inside the airtight Plexiglas chamber were measured with the LI-COR 6200 gas analysis system. The surface radiative temperature of the canopy and the air temperature inside the chamber were measured. A pair of LI-COR quantum sensors were used to measure the incident PAR flux density inside and outside the chamber. The chamber was momentarily removed between measurements to prevent heating of the substrate. A space blanket was placed over the chamber between readings. Stomatal resistance of selected species of the grass used to estimate the total canopy resistance were measured independently using a leaf diffusion porometer.
The FIFE study area, with areal 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.
Measurements were made at the five sites listed below:
SITEGRID STN NORTHING EASTING LATITUDE LONGITUDE ELEV SLOPE ASPECT -------- --- -------- ------- -------- --------- ---- ----- ------ 2043-PSB 44 4330003 713536 39 05 42 -96 31 51 415 2133-PSB 60 4329720 711521 39 05 34 -96 33 15 405 2655-PSB 36 4328787 716070 39 05 00 -96 30 07 367 4 E 4439-PSB 16 4325215 712794 39 03 07 -96 32 28 445 2 N 6943-PSB 28 4320147 713500 39 00 22 -96 32 04 415
The chamber covered an area of ground 1.8 m by 0.8 m.
Data were obtained from July 1, 1987 through October 12, 1987. A total of 25 days of usable data were obtained with the box during IFC-2, IFC-3, and IFC-4.
During each month, data were collected at an average of 3 days apart. Each time a site was visited, a series of observations were taken at half-hourly intervals for 4 to 6 hours.
The SQL definition for this table is found in the PHO_BOX.TDF file located on FIFE CD-ROM Volume 1.
Parameter/Variable Description Range Units Source
SITEGRID_ID This is a FIS grid location code. Site grid codes (SSEE-III) give the south (SS) and the east (EE) cell number in a 100 x 100 array of 200 meter square cells. The last 3 characters (III) are an instrument identifier.
STATION_ID The station ID designating the location of the observations.
OBS_DATE The date of the observations, in the format (DD-MMM-YY).
OBS_TIME The time that the observation was [GMT] taken in GMT. The format is (HHMM).
VAPOR_PRESS The vapor pressure within the box. [millibars]
AIR_TEMP The air temperature within the box. [degrees Kelvin]
SURFACE_TEMP The surface temperature. [degrees Kelvin]
PAR_DOWN The downward (incoming) [microEinst] Photosynthetically Active [meter^-2] Radiation (PAR). [sec^-1]
PHOTOSYN_RATE The photosynthesis rate (CO2 [mg of CO2] assimilation rate). [meter^-2] [sec^-1]
RESISTANCE The total canopy resistance, the [sec] plants resistance to the transfer [meter^-1] of water.
FIFE_DATA_CRTFCN_CODE ** The FIFE Certification Code for the data, in the following format: CPI (Certified by PI), CPI-??? (CPI - questionable data).
LAST_REVISION_DATE data, in the format (DD-MMM-YY).
Missing values are indicated by a -999, -999.9 or -999.99.
** Valid levels
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 that are "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 VAPOR_PRESS AIR_TEMP ----------- ---------- ---------- -------- ----------- -------- 2043-PBS 44 06-OCT-87 1529 4.90 292.90 2043-PBS 44 06-OCT-87 1558 4.46 293.47 2043-PBS 44 06-OCT-87 1636 4.37 295.40 2655-PBS 36 12-OCT-87 2115 7.29 305.93 SURFACE_TEMP PAR_DOWN PHOTOSYN_RATE RESISTANCE FIFE_DATA_CRTFCN_CODE ------------ -------- ------------- ----------- --------------------- 293.92 947.0 .5940 1585.8300 CPI 295.63 1122.0 -4.2281 1122.1800 CPI 297.83 1197.0 -3.9848 1916.8200 CPI 300.51 698.0 -3.2340 2167.7700 CPI LAST_REVISION_DATE ------------------ 14-MAR-89 14-MAR-89 14-MAR-89 14-MAR-89
The Canopy Photosynthesis data were collected at an average of 3 days apart. Each time a site was visited, a series of observations were taken at half-hourly intervals for 4 to 6 hours.
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.
Sellers et al. (1990) used the following mass conservation equation (Eq. 1) and canopy/surface resistance equation (Eq. 2) to produce a set of net CO2 flux and surface resistance estimates.
CO2 assimilation rate:
A = (-12.031/Ta) * (Vb/Ab) [P * (dC/dt) + (C/P) * (de/dt)] (Eq. 1)
A = assimilation rate, [mmol][m^-2][s^-1]
C = CO2 conc., [ppm]
Ta = air temperature, [degrees K]
e = vapor pressure, [mb]
Vb = box volume, [m^3]
Ab = ground surface area, [m^2]
P = atmospheric pressure, [mb]
t = time
Equation (1) can be solved in two ways:
(i) Derivative: A line fit is made to the time-series of CO2 data. This yields dC/dt and hence A.
(ii) Integrative: Both sides of (Eq. 1) are integrated with time so that the start and end values of C and e are used to get an average estimate of A. This can be done over different portions of the time series of data.
Canopy/surface resistance (rc):
dqa/dt = (rho*Cp) / (lamda*gamma) [(es(Ts)-e) / (rb+rc)] Ab/Vb (Eq. 2)
qa = mixing ration inside box, [kg][kg^-1]
rho = density, [kg][m^-3]
cp = specific heat of air, [J][kg^-1][K^-1]
gamma = psychrometric constant, 0.66 [mb][K^-1]
lamda = latent heat of vaporization, [J][kg^-1]
es(Ts) = saturated vapor pressure at surface temperature (Ts), [mb]
rb = aerodynamic resistance between foliage and air in box, [sec][m^-1]
rc = canopy/surface resistance, [sec m^-1]
t = time
In (Eq. 1), the solution of C(t) is essentially linear. In (Eq. 2), the increase in water vapor suppresses further evapotranspiration so qa(t) is exponential. The calculation of the combined term ( rb + rc ) is then given by three methods.
(i) Derivative: Exponential fits to the time-series of qa, Ts and e. Derivatives of the fits are used to solve (Eq. 2).
(ii) Line fit: The time-constants for qa(t) involve terms from the right-hand side of (Eq. 2).
(iii) Integrative: Both sides of (Eq. 2) are integrated numerically with time. Aerodynamic resistance between foliage and air in box and canopy/surface resistance are assumed constant over this period.
Photosynthesis rates and canopy resistance were computed by:
Errors could result from calibration drift of the LI-COR 6200 gas analyzer, dust on chamber surface during measurements, or a gas leak of the box.
Data were validated by intercomparison with Surface flux data and other Surface Radiance Biology data sets.
Data showed expected trends, but quantitative accuracy is uncertain.
No quantitative assessment was made.
Other errors mentioned in the Sources of Error Section were not assessed.
FIS staff applied a general Quality Assessment (QA) procedure to these 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 data sets 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 data set. 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.
It is probable that this device underestimates C02 assimilation rates by underestimating gas concentration.
The dust, which accumulated on the chamber surfaces, may have reduced PAR levels, slightly.
These data can be compared with the Leaf Photosynthesis data and with the surface flux measurements.
The major variables among the five sites selected for detailed study were soil type, management practices (burned, unburned, grazed, and ungrazed grassland), and topography. The dominant grass species were Andropogon gerardii, Andropogon scoparius, and Sorghastrum nutans.
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 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 Canopy Photosynthesis 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 .PSB for this data set.
Farquhar, G.D., and T.D. Sharkey. 1982. Stomatal conductance and photosynthesis. Ann. Rev. Plant Physiol. 33:317-345.
Asrar, G., M. Fuchs, E.T. Kanemasu, and J.L. Hatfield. 1984. Estimating absorbed photosynthetic radiation and leaf area index from spectral reflectance in wheat. Agron. J. 76:300-306.
Polley, H.W., J.M. Norman, T.J. Arkebauer, W.A. Walter-Shea, D.H. Greegor and B. Bramer. 1992. Leaf gas exchange of Andorpogon gerardii Vitman. Panicum virgatum L. and Sorghastrum nutans (L) NASH in a tallgrass prairie. J. Geophys. Res. 97:18,837-18,844.
Sellers, P.J. 1985. Canopy reflectance, photosynthesis and transpiration. Int. J. Remote Sens. 6:1335-1372.
Sellers, P.J. 1985. Canopy reflectance, photosynthesis and transpiration. II. The role of biophysics in the linearity of their interdependence. Remote Sens. Environ. 21:143-183.
Sellers P.J., F.G. Hall, D.E. Strebel, R.D. Kelly, S.B. Verma, B.L. Markham, B.L. Blad, D.S. Schimel, J.R. Wang, and E.T. Kanemasu. 1990. FIFE Interim Report. NASA Internal Document. No. 623. NASA Goddard Space Flight Center. Greenbelt, Maryland.
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 http://daac.ornl.gov/acronyms.html.
April 25, 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.
Asrar, G., and P. J. Sellers. 1994. Canopy Photosynthesis Rates (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/27. 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).