Common infrastructure data from the HYREX project

Go to: [ Contents | Introduction | Data | Transfer | End ]


  1. Introduction
  2. Instruments and data
  3. Transferring HYREX data from the BADC

Go to: [ Contents | Introduction | Data | Transfer | End ]

1. Introduction

This dataset comprises data gathered from instruments, located in and around the HYREX experimental catchment, that constitute a common infrastructure providing data for use by all HYREX projects. The data are made available to HYREX researchers via a central archive maintained by the CEH Wallingford (formerly the Institute of Hydrology (IH)).

The Unified Model data, the vertically pointing radar and associated datasets supplied by the University of Salford, and Chilbolton radar data are described in separate documents.

1.1 The HYREX experimental catchment

The River Brue catchment in Somerset, south-west England, drains an area of 132 sq. km to its river gauging station at Lovington. The catchment is predominantly rural and of modest relief, with spring-fed headwaters rising in the Mendip Hills and Salisbury Plain. Clays, sands and oolites give rise to a responsive flow regime. The catchment is scanned continuously by two Met. Office network C-band radars, one at Wardon Hill and the other at Cobbacombe Cross (Doppler), located at ranges of circa 40 and 70 km from the centre of the catchment respectively. The radars record data from the lowest elevation scan at 5 minute intervals for a 2 km grid out to a range of 75 km. Data for a 5 km grid out to a range of 210 km are available for four scan elevations, including the lowest one. A third radar, at Chilbolton in Hampshire at a range of about 75 km, is deployed during special intense observing periods and provides a Doppler dual polarisation S-band capability.

1.2 Experimental infrastructure

The common experimental infrastructure comprises the national network radars at Wardon Hill and Cobbacombe Cross, a purpose-built dense raingauge network, an automatic weather station (AWS), an automatic soil water station (ASWS) and a river gauging station. This part of the infrastructure was provided by the Meteorological Office, the Environment Agency, the Natural Environment Research Council, and the Ministry of Agriculture, Fisheries and Food (MAFF). These instruments have provided a continuous record throughout HYREX. A disdrometer, operated by CEH Wallingford, was deployed during selected Intense Observing Periods.

1.3 Research using the data within HYREX

CEH Wallingford was responsible for the quality control of the dense raingauge network as part of its project concerned with the accuracy of radar/raingauge networks. It also made use of disdrometer data to better understand how the relation between radar reflectivity and rain-rate was affected by the raindrop size distribution.

The University of London consortium were also major users of the dense raingauge network in the context of carrying out basic statistical analyses of both raingauge and radar data. Their primary interest lay in the use of the network weather radar data for modelling the space-time structure of rainfall field for hydrological design applications.

The University of Newcastle employed both the dense raingauge data and network radar data for developing and evaluating a stochastic space-time rainfall forecasting system; they also used catchment flow data to develop a rainfall-runoff model for the catchment in order to convert forecasts of rain to flow.

CEH Wallingford, in collaboration with JCMM, used multi-scan network radar data (along with Unified Model output data) in their development of a storm model for short-term rainfall forecasting.

Go to: [ Contents | Introduction | Data | Transfer | End ]

2. Instruments and data

The HYREX instruments and the data they record are described below, along with comments on additional derived data and data quality information. The format and content of data files are summarised briefly, and full details of data records and fields may be found in the file /badc/hyrex/data/Common/FORMATS. The data files themselves are located in the various instrument subdirectories of /badc/hyrex/data/Common.

2.1 Weather radar

The Wardon Hill and Cobbacombe Cross radars operate at the C-band wavelengths that are standard for the UK weather radar network. Each radar completes one azimuthal scan every minute, and cycles through 4 different scan elevations (0.5, 1.0, 1.5 and 2.5 degrees) every 5 minutes. Software at the radar site converts measurements of reflectivity on a radial grid into measurements of rainfall intensity on two Cartesian grids: an 84x84 grid of 5km square pixels covering a radius of 210km and a 76x76 grid of 2km square pixels covering a radius of 76km. Rainfall intensity is digitised into 208 levels ranging semi-logarithmically from 1/32 to 126 mm/h. Only the Cartesian-grid rainfall intensity data are recorded, with data available for all scan elevations on the 5km grid, but only for the lowest scan ("beam 0") on the 2km grid. The Brue catchment lies within the 2km grid for both radars.

There is one instrument directory for each radar (war and cob). The image data are stored in ASCII files, one file per radar per day, in the order in which they were observed. The data files have names constructed from the date and radar name, such as 19950425_war_ih or 19941105_cob_ih (the ih suffix indicates that the files are in the format used by CEH Wallingford, formerly the Institute of Hydrology), and are located in monthly directories within each instrument directory (e.g. war/9504 or cob/9411). For each data file there is a corresponding log file (suffix lg) that lists the images and other data contained in the data file. A FORTRAN subroutine, readri.f, is provided that will read a specified image from a given data file into a FORTRAN array.

Each instrument directory has a QUALITY subdirectory, containing text files of information related to data quality. In particular, the files named missing.txt summarise periods of missing data.

The radar data have been used to calculate catchment-average rainfall over 15-minute and daily accumulation periods. These data are held in the directory catch_avgs/radar.

Go to: [ Contents | Introduction | Data | Transfer | End ]

2.2 Dense raingauge network

The dense raingauge network comprises 49 Cassella 0.2mm tipping bucket raingauges, each recording time of tip to a time resolution of 10 seconds. The network provides at least one raingauge in each of the 2km radar grid squares that lie entirely within the catchment. In addition, there are two parallel lines of greater gauge density extending SW to NE across the catchment, aligned with the prevailing wind direction and running from lowland to upland. Within each line there is one 2km grid square containing a super-dense sub-network of 8 raingauges arranged in a square-within-a-diamond configuration, with one sub-network in a lowland area and the other in an upland area.

The raingauges are identified by four-letter abbreviations; details and locations of the raingauge sites may be found in the instrument directory drn. The data are held in monthly files with names such as 9407_drn or 9511_drn. Each file lists all tips from all gauges, listed in alphabetical order of raingauge abbreviation, and chronologically within each gauge.

The drn/QUALITY directory contains two text files, one listing all the known or inferred faults with each raingauge, and the other summarising the periods for which each raingauge is considered to provide valid data. There is also a Microsoft Excel file, download.xls, containing summary totals and notes made on each occasion that data were downloaded from the raingauge loggers.

The raingauge data and quality information have been used to calculate catchment-average rainfall over 15-minute and daily accumulation periods. These data are held in the directory catch_avgs/raingauge.

2.3 Automatic weather and soil water stations

An automatic weather station (AWS) and automatic soil water station (ASWS) are located close to the Bridge Farm raingauge in the lowland sub-network. The AWS records solar and net radiation, wet and dry bulb temperature, wind speed and direction, atmospheric pressure and rainfall (0.2mm tip) every 15 minutes, and also records daily totals or averages. The ASWS makes hourly capacitance probe, pressure transducer and temperature measurements at three depths, along with rainfall (0.5mm tip).

The data are held in yearly files within each instrument directory aws or asws). AWS and ASWS data file formats are very similar, differing only in the number and interpretation of the data fields on each line. The files of ASWS hourly data have names of the form 95_brfm; the AWS 15-minute data files are of the form 95_bfrm_min, with the corresponding daily data in 95_bfrm_day (bfrm refers to the instrument location at Bridge Farm).

The ASWS probes have not been calibrated at site, except for the one occasion listed in the asws/CALIBRATION file.

Very limited data quality information may be found in the QUALITY text file in the AWS instrument directory, and in the QUALITY directory in the ASWS instrument directory.

Go to: [ Contents | Introduction | Data | Transfer | End ]

2.4 Disdrometer

The disdrometer is located close to the AWS, but has been deployed only during certain HYREX Intense Observing Periods (IOPs). It records the number and beam occupation time of raindrops in 16 drop-size 'bins', with a sampling interval of between 10 and 60 seconds.

Each data file in the disdrometer instrument directory dis contains one hour of disdrometer data, where the hour is identified by the file name (e.g. d95090805). The only quality note is that sample time stamps (and file name times) during the summer months are BST and not GMT.

2.5 River gauging station

The River Brue is gauged at the catchment outlet at Lovington (UK Surface Water Archive no. 52010). River level is recorded every 15 minutes and is converted to flow using a well-established rating equation. Both levels and flows are held in the dataset, and the record extends for nearly 8 years before the start of HYREX.

The text file RATING_lov in the river gauging station instrument directory rgs) lists the rating equation coefficients. Each data file contains one year of data, and has a name of the form 95_lov. The QUALITY text file contains a few notes on missing data.

2.6 Land use data

LandSat data have been used to derive 5 classes of land use (urban, grass, arable, forest, water) on a 50m pixel grid covering the catchment. It is possible that other digitised geographic data for the HYREX experimental catchment may be made available at a later date.

The data are held in the file landuse/brueland.dat, whose format is described in the text file landuse/brueland.txt.

Go to: [ Contents | Introduction | Data | Transfer | End ]

3. Transferring HYREX data from the BADC

The common infrastructure dataset filenames, formats and directory structures have been maintained in adding the data to the BADC data directories. All of the datasets described here are supplied in ASCII files. Most files are compressed with the standard UNIX compress utility (adaptive Lempel-Ziv encoding) although some are plain ASCII text. UNIX compressed (.Z suffix) files can be uncompressed using the standard public domain program gzip.

3.1 Before you start

You may need gzip installed on your local system to uncompress some of the data files - the source code is available from software archives. You will also need to know how to use gzip once you have the files on your system.

3.2 Transferring and unpacking files

With the exception of the UKMO-suplied radar datasets, all files may be transferred either directly from these WWW pages, or via FTP FTP. FTP is probably more efficient for downloading a large number of files. The UKMO files may only be FTP'd from a named BADC account (see under Restricted Data on the HYREX welcome page).

All the data are in ASCII files compressed using the standard UNIX compress utility. The documentation and software files are uncompressed ASCII files, with the exception of download.xls.Z, which is a compressed Microsoft Excel 6.0 file containing field reports on raingauge data. Use UNIX uncompress, GNU gzip, or an equivalent utility to unpack them.

Go to: [ Contents | Introduction | Data | Transfer | End ]

3.3 Finding data, documentation and software files

HYREX common infrastructure data, documentation and software files are located beneath the directory /badc/hyrex. Here you will find a README file and the following subdirectories

The data directory contains a subdirectory for each of the instruments, along with several text files describing the organisation and format of the data files. Each instrument directory contains the appropriate data files (subdivided into monthly directories for the two radars) and additional text files relating to data quality.

The doc directory structure mirrors the data directory tree, but it contains only documentation (text) files. Most of these files are simply links to the corresponding files in the data directory tree.

The software directory contains software for reading the data files. The only such software is that used to read the radar data, located in the software/readrad directory.

3.4 Using the data

Read the data/Common/NEWS file for latest data news.

Read the data/Common/FORMATS file for a detailed description of the data records and fields in each type of data file.

The raingauge, catchment-average rainfall, AWS, ASWS, and river gauging station data are in simple tabular formats and should be straightforward to load into most spreadsheets or databases.

Simple programs may need to be written to handle the radar, disdrometer and landuse data. A FORTRAN subroutine for reading the radar data can be found in software/common/readrad.