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Thorney Island

 

Location

Thorney Island is a peninsula of land extending into Chichester Harbour, on the south coast of England. The remote sensing test site is located at 50 º 49'N, 00 º55'W.

Location of the Thorney Island test site

Figure 1.
Location of the Thorney Island test site. (© NCAVEO, 2005).

Introduction

Thorney Island was a true island until the 19th century, but it is now connected to the mainland by a causeway of reclaimed land. The geography of the site restricts access onto the island, and this is further controlled by the fact that most of the island is a military base. The single access road is controlled by a checkpoint and a permit is necessary to work on the site. A public footpath follows the coastline around the island, but this allows no access to the interior of the island. The area is popular with walkers and ornithologists as Chichester harbour is an internationally important area for migrating birds. The island is flat and rises to little more than ?? metres above sea level.

The main remote sensing test site on Thorney Island is part of a disused airfield that covers most of the island. Most of the runways and areas of hardstanding are intact and accessible by a vehicle, once the necessary permissions have been gained. The primary focus of remote sensing research at the site has been airborne sensor calibration and experiments in atmospheric correction, but there has also been research on remote sensing of the intertidal sediments around the island, particularly the area known as Pilsea Sand to the south of Thorney Island.

Landsat TM images of Thorney Island  Landsat TM images of Thorney Island

Figure 2.
Landsat TM images of Thorney Island.
(left-hand image is summer, right-hand is winter)
(© NASA, 19??).

Aerial photograph of Thorney Island

Figure 3.
Aerial photograph of Thorney Island (© NERC, 1994).

Projects: Overview

Remote sensing research at Thorney Island began in the early 1990s, with a study by researchers from UCL which used data from an airborne multispectral scanner to investigate outflow from a sewage works located in the north of the island. This was followed in the mid-1990s by a study by scientists from the Ministry of Agriculture, Fisheries and Food (MAFF) and the University of Southampton to investigate the grazing behaviour of Brent geese (??) which normally overwinter on the salt marsh. As part of this study a number of experimental grass plots were established on Thorney Island and their spectral reflectance monitored over 12 months. Areas of concrete and asphalt on the disused airfield were used as control surfaces for this work.

The asphalt and concrete surfaces of the main runways were investigated further during 1999, when a series of field spectral measurements were made using multiband radiometers. This led to the designation of four sub-sites with different reflectance properties : TNA (Thorney Northern Asphalt), a small area of virtually black asphalt; TSA (Thorney Southern Asphalt), a larger area of spatial uniform mid-grey asphalt; TSC (Thorney Southern Concrete), an area of large rectangular concrete slabs and TSG (Thorney Southern Grass) an area of spatially uniform short grass adjacent to the main N-S runway.

Instruments on the Thorney Southern Concrete site in May 1999

Figure 4.
Instruments on the Thorney Southern Concrete site in May 1999. (© NCAVEO, 2005)

The airfield is disused but the areas of grass around the runways are regularly mown, keeping the grass canopy short and homogeneous.

Gary Llewellyn engaged in a vegetation survey of the Thorney Southern Grass site

Figure ?.
The Thorney Southern Grass site. A high-risk area for contact lens wearers. (© NCAVEO, 2005).

Red and NIR reflectance of the Thorney Island calibration sites on several dates during May 1999

Figure ?.
Red and NIR reflectance of the Thorney Island calibration sites on several dates during May 1999. (© NCAVEO, 2005).

Interest in the site for calibration purposes led to an experiment in July 2001 in which high-quality spectral ground data were collected simultaneous with an overflight by the NERC Airborne Remote Sensing Facility, operating an Itres Instruments Compact Airborne Spectrographic Imager (CASI). The data collected on this occasion are described in detail here and this data set may be obtained from the NCAVEO office.

Valeria Salvatori and Nick Hamm collecting spectral data on the Thorney Southern Concrete site

Figure ?.
Valeria Salvatori and Nick Hamm collecting spectral data on the Thorney Southern Concrete site. (© NCAVEO, 2005).

During 2002-2004 the site was the focus of a PhD study by Karen Anderson which investigated the temporal dynamics of two of the calibration surfaces in particular (TSC and TSA). A high precision dual-beam field spectroradiometer was constructed for this purpose and results obtained with this showed systematic variability in the reflectance of this surface over different time scales (Anderson, 2005).

Bill Damon measuring the diffuse-to-global ratio using a mobile dual-beam spectroradiometer

Figure ?.
Bill Damon measuring the diffuse-to-global ratio using a mobile dual-beam spectroradiometer. (© Karen Anderon, 2003).

 

In 200? the site was designated one of several test sites for the Compact High Resolution Imaging Spectrometer (CHRIS) on-board the ESA PROBA satellite. Three PROBA-CHRIS data sets have been collected to date and one of these is described further in the section of this website on atmospheric correction (Example 2).

A set of five PROBA-CHRIS images of Thorney Island collected on 7th October 2004

Figure ?.
A set of five PROBA-CHRIS images of Thorney Island collected on 7th October 2004. These images were acquired with different view zenith angles, as follows:
Centre image : nadir
Top-left :
Bottom left :
Top right :
Bottom right :
Data have been provided by the European Space Agency, using the ESA PROBA platform and the SIRA Technology Ltd CHRIS instrument, developed with support from BNSC. © Sira Technology / ESA 2004.

 

Current remote sensing research at the site (2005)

Two airborne sensor campaigns are planned this summer:

  1. A test flight of a quad-polarised airborne SAR system recently developed by EADS Astrium.
  2. A test flight of a CASI-3 system newly acquired by the UK Environment Agency.

 

Links for further information

Thorney Island 24 July 2001 data set

Thorney Island airborne remote sensing database

Chimet : meteorological data from a buoy in Chichester Harbour

History of the airfield on Thorney Island

Birdlife of Chichester Harbour

 

Key contacts for the Thorney Island site

Principal Investigator : Professor Ted Milton, School of Geography, University of Southampton, Southampton SO17 1BJ, UK.

Some publications based on research at Thorney Island

  1. Anderson, K., Milton, E. J. and Rollin, E. M., 2002. Towards an operational method to calibrate casi data to reflectance using ground-based methods. NERC Airborne Remote Sensing Workshop, Rutherford Appleton Laboratory, Didcot, Oxfordshire, Natural Environment Research Council, Swindon, CD-ROM.
  2. Anderson, K., Milton, E. J. and Rollin, E. M., 2003. Sources of uncertainty in vicarious calibration: understanding calibration target reflectance. Proceedings of the International Geoscience and Remote Sensing Symposium (IGARSS), Toulouse, France, Institute of Electrical and Electronics Engineers (IEEE), New York, CD-ROM.
  3. Anderson, K., Milton, E. J. and Rollin, E. M., 2003. The temporal dynamics of calibration target reflectance. Scales and dynamics in observing the environment, Remote Sensing and Photogrammetry Society, Nottingham, UK, CD-ROM.
    Anderson, K., Milton, E. J. and Rollin, E. M., in press. Calibration of dual-beam spectroradiometric data. International Journal of Remote Sensing.
  4. [Karen PhD]
  5. [Patrick Friend thesis and papers]
  6. Hamm, N., Atkinson, P. M. and Milton, E. J., 2001. Uncertainty in remote sensing models. Proceedings of the RSPSoc2001 Conference on Geomatics, Earth Observation and the Information Society, Remote Sensing and Photogrammetric Society, Nottingham, CD-ROM.
  7. Hamm, N., Atkinson, P. M. and Milton, E. J., 2002. Resolving the support when combining remotely sensed and field data: the case of atmospheric correction of airborne remotely sensed imagery using the Empirical Line method. Fifth International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, Melbourne, Australia, 339-347.
  8. Hamm, N., Atkinson, P. M. and Milton, E. J., 2003. The combined effect of spatial resolution and measurement uncertainty on the accuracy of empirical atmospheric correction. Proceedings of the International Geoscience and Remote Sensing Symposium (IGARSS), Toulouse, France, Institute of Electrical and Electronics Engineers (IEEE), New York, CD-ROM.
  9. Hamm, N., Atkinson, P. M. and Milton, E. J., 2003?. Evaluating the effect of positional uncertainty in field measurements on the atmospheric correction of remotely sensed imagery. Geostatistics for Environmental Applications. Sánchez-Vila, X. and Carrera, J. Dordrecht, Netherlands, Kluwer.
  10. Milton, E. J. and Emery, D. R., 1995. The identification of reference endmembers using high spatial resolution multispectral images. Remote Sensing in Action. Proceedings of the 21st Annual Conference of the Remote Sensing Society, Nottingham, Remote Sensing Society, 579-586.
  11. Milton, E. J., 1999. Image endmembers and the scene model. Canadian Journal of Remote Sensing 25, 112-120.
  12. Milton, E. J., 2000. Practical methodologies for the reflectance calibration of casi data. Activities of the NERC Equipment Pool for Field Spectroscopy (EPFS) in support of the NERC Airborne Remote Sensing Facility. Southampton, UK, NERC-EPFS, Department of Geography, University of Southampton, 14pp.
  13. Milton, E. J., Razak, A. and McKay, H. V., 1995. A polygon-based approach to land-cover classification for grassland management. Remote Sensing in Action. Proceedings of the 21st Annual Conference of the Remote Sensing Society, Nottingham, Remote Sensing Society, 285-292.
  14. Milton, E. J., Smith, G. M. and Lawless, K. P., 1996. Preparatory research to develop an operational method to calibrate airborne sensor data using a network of ground calibration sites. Second International Airborne Remote Sensing Conference and Exhibition, Ann Arbor, MI, ERIM, III, 132-141.
  15. Smith, G. M. and Milton, E. J., 1999. The use of the empirical line method to calibrate remotely sensed data to reflectance. International Journal of Remote Sensing 20, 2653-2662.

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© NCAVEO, 2005
Network for Calibration and Validation of Earth Observation data
School of Geography, University of Southampton
Southampton SO17 1BJ, UK

Last updated 15/02/2006
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