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Water Budget data

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Frequently-anticipated questions:


What does this data set describe?

Title: Water Budget data
Abstract:
The data set contains data for vapor pressure gradient, air temperature gradient, soil heat flux, water temperature top and bottom, net solar radiation, water level, air temperature, wind direction and speed, relative humidity, and pyronometer.
  1. How should this data set be cited?

    German, Edward R. , 2000, Water Budget data.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -80.82
    East_Bounding_Coordinate: -80.27
    North_Bounding_Coordinate: 25.76
    South_Bounding_Coordinate: 25.29

  3. What does it look like?

    <https://sofia.usgs.gov/publications/fs/168-96/> (GIF)
    location of ET stations and the Everglades

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: Oct-1995
    Ending_Date: Jan-1997
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Point data set. It contains the following vector data types (SDTS terminology):

      • Entity point (4)

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.1. Longitudes are given to the nearest 0.1. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    The parameters collected for the sites inclufe: vapor pressure gradient, air temperatue gradient, soil heat flux, water temperatue (top and bottom), net solar radiation, water level, air temperature, wind direction and speed, relative humidity, and pyronometer
    Entity_and_Attribute_Detail_Citation: USGS


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

    • Edward R. German

  2. Who also contributed to the data set?

    Dave Stannard, USGS NRP, Denver, Colorado, has provided project operation and data analysis during each year of the study.

  3. To whom should users address questions about the data?

    Ed German
    U.S. Geological Survey
    Project Chief
    12703 Research Parkway
    Orlando, FL 32826
    USA

    407 803-5517 (voice)
    egerman@usgs.gov


Why was the data set created?

Knowledge of the water budget of the Everglades (south Florida) system is crucial to the success of restoration and management actions. Although the water budget is simple in concept, it is difficult to assess quantitatively. Models used to simulate changes in water levels and vegetation that might result from various management actions need to account for all components of the water budget accurately.

In 1995, a study to measure and model ET in the Everglades was begun as part of the US Geological Survey South Florida Ecosystem Program. The principle objective of the study is to develop an understanding of ET within the Everglades drainage unit, excluding agricultural and brackish environments. To achieve this, a network of eight ET-measurement sites was established, representing the various types of hydrologic and vegetative environments. Continuous measurement of ET at these sites for at least a 2-year period (October 1995 through September 1997) is being used to develop regional models of ET that can be used to estimate ET at other times throughout the Everglades.


How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: 2000 (process 1 of 1)
    The Bowen-ratio energy budget method was selected for use in the Everglades. The components of the energy budget and other data necessary for application of the Bowen-ratio method were measured at 15-minute intervals. Net radiation, the difference between incoming shortwave (solar) radiation and outgoing shortwave and longwave radiation, was measured by using a net radiometer. Soil heat storage was estimated by using measured values of heat flux, soil temperature, and soil moisture, together with estimated values of soil bulk density and particle heat capacity. Storage of heat in water, which must be considered when the water level is above land surface, was estimated from measurements of water level and water temperature. The difference between the net radiation and the energy adsorbed by the water and soil gives the total amount of energy available for sensible heat transport and latent heat transport (composed of the latent heat of vaporization of water and the mass evaporation rate). Sensible heat is the heat associated with convective transport; latent heat is the heat required for changing water from a liquid to a vapor state.

    The Bowen ratio can be approximated as a function of vertical differences of temperature and vapor pressure in the air. At vegetated sites, air temperature and vapor-pressure measurements are made simultaneously every 30 seconds at two points that are several feet above the land surface and separated vertically by 3 to 5 feet (ft). Because the temperature and vapor-pressure differentials generally are small in comparison to sensor calibration bias, the upper and lower sensors are reversed in position every 15 minutes. This reversal of position makes it possible to eliminate the effect of sensor bias by averaging the differences in the mean measured air temperature and vapor-pressure differentials during two successive 15-minute intervals, and by using the resultant average differentials to compute latent heat transport at 1/2-hour intervals.

    At open-water sites with little or no emergent vegetation, the air temperature and vapor-pressure differentials are determined from measurements of water temperature at the water surface and air temperature and vapor pressure at a point 3 to 4 ft above the water surface. The water-surface temperature is measured by using a float-mounted thermocouple and is assumed to represent the air temperature at the water-air interface. The vapor pressure at that point is assumed to be equivalent to 100 percent relative humidity. Because the water-surface to air differences are much greater than differences in the air over similar distances, the effect of air and vapor pressure sensor bias is negligible. Therefore, the sensor exchange mechanism is not required and only one vapor pressure sensor is needed at such sites.

    A modified Priestley-Taylor model of ET was calibrated for each site. These individual site models were then combined into two regional models: one applicable to vegetated wet-prairie and sawgrass-marsh sites, and the other applicable to freshwater sloughs and other open areas with little or no emergent vegetation.

    The Priestley-Taylor model of evaporation is a semi-empirical model that expresses ET as a function of aerodynamic resistance (a function of wind speed, canopy characteristics, and atmospheric stability) and canopy resistance (a measure of stomatal resistance to vapor transport from plants). In the Priestley-Taylor model, the atmosphere is assumed to be saturated and an empirical term, the Priestley-Taylor coefficient (P-T), is added to account for the fact that the atmosphere does not generally attain saturation. Priestley-Taylor models were developed for the nine ET sites, in which the P-T coefficient was expressed as a function of incoming solar energy and water level. Only data for 1996-97 that passed screening tests for accuracy were used to develop the site models using equation 5. The screening tests were based on range limits, visual inspection of plotted net radiation, temperature and humidity readings to eliminate periods when sensors were obviously malfunctioning, and on the criteria that flux calculations are inappropriate if the calculated latent heat flux is not in the opposite direction from the observed vapor-pressure gradient. Such a situation would indicate an error in determination of either the energy budget or the vapor-pressure or temperature gradient. Resolution limits for this study are 0.013 degree Celsius for vertical temperature differences and 0.003 kPa for vapor-pressure differences. These screening criteria eliminated about one-half of the available data from model development, mostly because of sensor failure and resolution limits. Most of the data rejected because of resolution limits or flux directions were for night-time hours, when energy inputs, air-temperature gradients, and vapor-pressure gradients are all relatively low. Regression statistics and values for the coefficients were calculated for all nine sites.

    Both water level and incoming solar radiation were significant at the 95-percent level in explaining variation in the P-T coefficient at all sites. The sign of the first regression coefficient is positive for all sites, indicating that the P-T coefficient increases as water depth increases. At vegetated sites, the P-T coefficient decreases as incoming solar radiation increases. At open-water sites the P-T coefficient increases as incoming solar radiation increases.

    The effect of water depth on the P-T coefficient when the water surface is above the land surface might be related to the presence of dead plant debris on the land surface. The dead plant material that is above the water surface intercepts some of the incoming solar energy, thereby preventing it from heating the water surface and enhancing evaporation. Instead, the dead plant debris is heated, which enhances convective heat transport. During periods of high water when some dead plant debris is submerged, lesser amounts of the debris are exposed to solar heating, and the water surface receives a greater portion of the solar energy than during periods of lower water. As a result, the portion of solar energy that is transformed into latent heat could be directly proportional to the water level, as is indicated by the positive value of the water-level coefficient at all sites. When water level is below land surface, as occurred occasionally at two sites, the P-T coefficient ?is still related directly to water level. This might be because moisture availability at the land surface decreases as the water level declines.

    The inverse relation of the P-T coefficient to incoming solar energy at vegetated sites also could be an effect of the non-transpiring dead plant debris. Solar heating of this dead plant debris would be proportional to the quantity of incoming solar energy. This solar heating could result in an increased portion of the available energy being converted into sensible heat, at the expense of latent heat. Incoming solar energy and latent heat transport are directly related at two open-water sites.

    The presence of some common attributes among the individual Priestley-Taylor models indicates that a generalized form of the model could provide a reasonable estimate of ET at all sites. This indicates that a generalized (regional) model would be appropriate for evaluating ET at other areas in the Everglades with similar hydrologic and vegetation characteristics to the sites modeled in this study.

    The relation of the P-T coefficient to water level for solar intensities of 200 and 800 watts per square meter (watts/m 2 ) was plotted for all sites. The plots indicate that, at 200 watts/m 2 , the relations of the P-T coefficient ?to water level are similar but not identical among the sites. At higher solar-energy levels (800 watts/m 2 ), the plots of the P-T coefficient?as a function of water level define two obvious groups: open-water sites and vegetated sites. The large separation between the two site types (open water and vegetated) at the higher energy level indicates that a significant portion of the incoming solar energy at vegetated sites is used in heating plants and plant debris, with a resultant relative increase in sensible heat transport compared to latent heat transport.

    A generalized relation of the Priestley-Taylor coefficient to water level and incoming solar energy was developed for vegetated and open-water sites by using least-squares regression to fit a data set of the coefficients generated by the individual site models. The values of the coefficients were generated over a range of water level from -1 to 2 ft in 0.1-ft intervals and a range of incoming solar radiation from 0 to 1200 watts/m 2 in 100-watts/m 2 intervals.

    See reference Regional Evaluation of Evapotranspiration in the Everglades for mathematical formulas and more detailed results.

    Person who carried out this activity:

    Ed German
    U.S. Geological Survey
    Project Chief
    12703 Research Parkway
    Orlando, FL 32826
    USA

    407 803-5517 (voice)
    egerman@usgs.gov

  3. What similar or related data should the user be aware of?

    German, Edward R. , 2000, Regional Evaluation of Evapotranspiration in the Everglades (2000): Water Resources investigations Report WRIR 00-4217, U.S. Geological Survey, Tallahassee, FL.

    Online Links:

    German, E. R., 1999, Regional Evaluation of Evapotranspiration in the Everglades (1999): Third International Symposium on Ecohydraulics Proceedings, International Association for Hydraulic Research, Salt Lake City, UT.

    Online Links:


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    Missing values in the data are shown as -123456E20. Data is available for 1995-1997 for Old Inghram Highway near Flamingo, FL, Shark Valley Slough site P33, and Everglades near Sweetwater, FL. Data for C111is available only for 1997.

  5. How consistent are the relationships among the observations, including topology?

    not applicable


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None.
Use_Constraints: none

  1. Who distributes the data set? (Distributor 1 of 1)

    Heather S.Henkel
    U.S. Geological Survey
    600 Fourth St. South
    St. Petersburg, FL 33701
    USA

    727 803-8747 ext 3028 (voice)
    727 803-2030 (FAX)
    hhenkel@usgs.gov

  2. What's the catalog number I need to order this data set?

    water budget data

  3. What legal disclaimers am I supposed to read?

    No warrantees are implied or explicit for the data

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 08-Nov-2006
Metadata author:
Heather Henkel
U.S. Geological Survey
600 Fourth Street South
St. Petersburg, FL 33701
USA

727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)
sofia-metadata@usgs.gov

Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)


This page is <https://sofia.usgs.gov/metadata/sflwww/germanwb_data.faq.html>

U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
Comments and suggestions? Contact: Heather Henkel - Webmaster
Generated by mp version 2.8.18 on Wed Nov 08 11:35:17 2006