Readme.tdr ---------- The TARRAWARRA DATA SET ----------------------- COLLECTED BY: Dr Andrew Western and Dr Rodger Grayson Centre for Environmental Applied Hydrology Department of Civil and Environmental Engineering The University of Melbourne Parkville 3052 Australia fax: +61 3 9344 6215 email: a.western@engineering.unimelb.edu.au r.grayson@engineering.unimelb.edu.au ******************* Copyright ************************** Copyright (c) 1995-1998 Centre for Environmental Applied Hydrology, The University of Melbourne. Permission to use, copy and distribute this data and its documentation, for non-commercial purposes, is hereby granted without fee, provided that the above copyright notice appear in all copies, that both that copyright notice and this permission notice appear in supporting documentation, and that any publication resulting from the use of this data cites: A W Western and R B Grayson, "The Tarrawarra data set: Soil moisture patterns, soil characteristics and hydrological flux measurements", Water Resources Research, in review. Authors are requested to forward 2 copies of any publication utilising this data set to the address above. Any problems with interpreting the data or requests for further information should be addressed to Dr Andrew Western or Dr Rodger Grayson. ****************************************************************** Acknowledgments --------------- The Tarrawarra catchment is owned by the Cistercian Monks (Tarrawarra) who have provided free access to their land and willing cooperation throughout the project. Funding for this work was provided by: the Australian Research Council (project A39531077); the Cooperative Research Centre for Catchment Hydrology; Oesterreichische Nationalbank, Vienna (project 5309); the Department of Industry, Science and Technology, International Science and Technology Program; The University of Melbourne and The Ian Potter Foundation. The European Space Agency and the National Aeronautical and Space Agency provided SAR data free of charge. Assistance in the field and with data processing has been provided by Karen Moore. Field assistance has also been provided by Jenny Barkley, Alison Dedman, Judy Dunai, Sarah Ewing, Brian Finlayson, Myriam Ghali, Tim Green, Veronique Gomendy, Tony Ladson, Lee Heng, Natasha Heron, Neela Janakiramanan, Loic Mangeot, Tom McMahon, Graham Moore, Joorst Overbeek, Michael Roberts, Kate Smolenska, Hugh Turral, Mariska te Vaarwerk, Jeff Walker, Fred Watson, Garry Willgoose, Mark Wood, and Rodger Young. Garry Willgoose, Tom McMahon, Günter Blöschl, David Goodrich, Hugh Turral, and Brian Finlayson have provided useful suggestions on the field data collection. Veronique Gomendy and Hugh Turral assisted with interpretation of the soil cores. Graham Moore has provided help with instrumentation on the DCV. Fred Watson provided advice on GIS and data management. ------------------------------------------------------------------ Time Domain Reflectometry Data ------------------------------ Soil moisture maps have been collected at Tarrawarra using Time Domain Reflectometry on 13 occasions. Soil moisture measurements were made using the following methods: Soil moisture measurements were made using an all terrain data collection vehicle (DCV) fitted with a position fixing system, Time Domain Reflectometry (TDR) soil moisture sensors, hydraulic systems for inserting the sensors, a computer for directing the operator to the desired sampling location and for logging data, and a variety of subsidiary equipment [Tyndal-Biscoe, 1994, Western et al., 1996]. The position fixing system allows measurements to be taken within 0.5 m of the planned location. Soil moisture measurements were made by driving the DCV to the required location, inserting the TDR probes with the hydraulic insertion system, taking a reading, removing the probes and moving on to the next location. Either one or four probes were used to make the measurements. When four probes were used they were mounted at the corners of a 1.7 m by 1.9 m rectangle. A TRASE system TDR [Soil Moisture Equipment Corp., 1989] fitted with 30 cm, two-wire probes mounted in standard TRASE Baluns, was used for the soil moisture measurements. On occasions when we used four TDR probes, they were connected to the TDR via a TRASE multiplexer. Probes were regularly inspected to ensure they had not been bent or damaged, and were either straightened or replaced if necessary. We monitored the soil moisture measurements as they were collected and repeated any anomalously high or low measurement, having moved the sample location slightly (by approximately 10 cm). Usually these repeated measurements were similar to the original measurement, in which case we retained the original measurement as the soil moisture recorded for that site. If there was a significant discrepancy (more than 2% by volume) the second measurement was used to represent the soil moisture at that location. The TDR measurements were made on regular grids. On most occasions a single TDR probe was used to make measurements on a 10 by 20 m grid oriented with the 20 m dimension along the long axis of the catchment (i.e. approximately east-west). The measurements were collected starting at the western end of the catchment and moving alternately north and south along neighbouring rows. Measurements were completed for each paddock in turn and were generally collected within a 15 hour period (each measurement has the date and time of measurement associated with it). We have also collected one set of measurements on the 10 by 20 m grid using four probes and one set on a 10 by 10 m grid using a single probe. Available soil moisture maps are summarised in the table below. Nature of the data ------------------ TDR measures the apparent dielectric constant of the soil-water- air media by measuring the time taken for a pulse of microwave energy to travel along the TDR probe. For our measurements, the measurement volume can be approximated by a cylinder 5 cm in diameter and 30 cm in length; however, the measurement process leads to a weighting of the measurement toward the soil nearest the wires of the probe. The apparent dielectric constant is then converted to a volumetric soil moisture using an appropriate calibration. The measured soil moisture represents the average soil moisture in the top 30 cm of the soil profile. We conducted a calibration of the TDR against gravimetric measurement of soil moisture to ensure the accuracy of our data. We did this by measuring the soil moisture using the TDR under typical field conditions, then taking a soil sample for which we determined the moisture content in the laboratory using standard gravimetric techniques. Soil samples were taken either using a coring device or by auguring a sample. The sample was taken over a depth of approximately 30 cm at the point where the TDR measurement was made. The volume of the soil sample was estimated either from the diameter of the corer and the length of the core or by finding the volume of water required to fill the hole remaining after an augured sample was taken. In the later case, we compared the volume with the volume estimated from the diameter of the augured hole and the depth of the hole. The variance of the differences between the gravimetric and TDR soil moisture measurements is 6.6(%V/V)^2. The error variance in the gravimetrically determined volumetric soil moisture are likely to be about 3(%V/V)^2, and is mainly due to uncertainty in determining the measurement volume. This implies a random error variance in the TDR derived estimates of soil moisture of 3(%V/V)^2. Geostatistical analyses [Western et al., submitted to J. Hydrology] confirm this (nuggets are typically 3(%V/V)^2). Errors in the TDR measurements can occur when measurements are made below significant surface water i.e. in the drainage lines when there is significant overland flow there. This is thought to be due to slight gaps (due to the soft (wet) soils) filling with water. This problem is apparent in data from the 2 and 20 September, 1996. For some analyses, truncation of the data to a maximum moisture of about 55%V/V would be justified. Data Availability ----------------- Date Sample grid -------------------------------------------------------- 25-27 September 1995 10x20m, 1 probe 13-14 February 1996 10x20m, 1 probe 22-23 February 1996 10x20m, 1 probe 28 March 1996 10x20m, 1 probe 13 April 1996 10x20m, 1 probe (a) 22 April 1996 10x20m, 1 probe 2-3 May 1996 10x20m, 4 probes (a) 3 July 1996 10x20m, 1 probe 2 September 1996 10x20m, 1 probe 20 September 1996 10x20m, 1 probe (a) 25 October 1996 10x20m, 1 probe (a) 10-11 November 1996 10x10m, 1 probe (b) 29 November 1996 10x20m, 1 probe (a) ------------------------------------------------------------------ (a) coincident with ERS1 and/or ERS2 SAR (b) coincident with NASA AirSAR File naming ----------- The TDR data is provided in separate files for each sampling. The file name convention is smddmmyy.tdr, where dd is day, mm is month, and yy is year. File format ----------- header: contains information on the grid, number of points, measurement depth, coordinate system, etc data records: the data is provided with one line per measurement and each data record contains date, time, x, y, dielectric constant, moisture. x and y are the coordinates of the measurement location in the Tarrawarra coordinate system (except for the transect which is in universal transverse mercator, zone 55) in units of meters. Moisture is percentage soil moisture determined on a volumetric basis. Files ----- Individual moisture patterns are contained in the files below. Archives of all the patterns are contained in (unix) patterns.tar.Z, (dos/windows) patterns.zip, and (macintosh) patterns.sit. individual patterns (ascii) sm270995.tdr sm140296.tdr sm230296.tdr sm280396.tdr sm130496.tdr sm220496.tdr sm020596.tdr sm030796.tdr sm020996.tdr sm200996.tdr sm251096.tdr sm101196.tdr sm291196.tdr