Harwood Forest is a coniferous plantation situated in the Northumberland National Park, 30 km inland from the North Sea coast. The site coordinates are: 55º 12' N, 02º 02' W. The forest grows on a gentle slope and has an elevation between 200 and 400 m.
Until the 1950s, when the plantation was created, the site was used for grazing. At present, the forest is dominated by Sitka spruce (Picea sitchensis) with smaller stands of Lodgepole pine (Pinus contorta). Neither species are native but were introduced from North America. The stands are very dense and only a small proportion of light reaches the understorey. Harwood Forest is used as a core site for validating EO products, especially those concerning gas exchange processes between the biosphere and the atmosphere. The flux tower on-site continously measures carbon dioxide and other gas fluxes over the Sitka Spruce stands.
Harwood Forest is part of the CARBO EUROPE Integrated project for understanding and quantifying the carbon balance of Europe and part of FLUXNET, a "network of regional networks" coordinating regional and global analysis of observations from micrometeorological tower sites. It is also a reference site for SpecNet (Spectral Network) project. This is a data-sharing cooperative aiming to add spectral measurements to existing flux tower sites around the world. Furthermore, SpecNet project aims to standardize sampling protocols and data structure across sites for a more effective modeling and validation of satellite data.
The University of Edinburgh operates the flux tower at Harwood Forest. This is a micrometeorological tower measuring the exchanges of carbon dioxide, water vapour and energy between the terrestrial ecosystem and the atmosphere.
The site has been studied extensively by the Earth Observation research group of CTCD (NERC Centre for Terrestrial Carbon Dynamics). They hold a wide range of data including airborne (ATM, CASI, Lidar, HyMAP, AirSAR) and spaceborne data (MODIS, SPOT-VGT, TM) as well ground measurements of LAI, canopy cover, soil and leaf reflectance, some directional measurements (BRDF) and detailed 3D measurements of plant structure. Helicopter measurements have been taken during 2003 and 2004 to measure top of canopy spectral reflectance.
Many of the remotely sensed data sets are complemented by simultaneous measurements of atmospheric optical depth and the reflectance of stable targets as well as with measurements of vegetation structural and radiometric properties.
Ground data have been collected since 2000 by staff from the University of Edinburgh and University College London and include:
- Canopy flux density: carbon dioxide, sensible heat, latent heat, water vapour, momentum, tree transpiration.
- Storage fluxes: canopy heat storage, CO2 storage in canopy air layer, latent heat and canopy air layer in canopy air layer.
- Soil fluxes: soil heat flux density, carbon dioxide flux density, soil evaporation.
- Meteorology: reflected radiation, global radiation, net radiation, diffuse radiation, photosynthetic photon flux density, light interception, air temperature, pressure, canopy radiative temperature, bole temperature, soil temperature 5cm and 30cm, relative humidity, wind direction, wind horizontal speed, atmosphere stability parameter, carbon dioxide concentration, water vapour concentration.
- Hydrology: precipitation, stemflow, throughfall, snow depth, soil water content (0-30cm, 40-70cm, 80-110cm).
- Biology and physiology: photosynthetic max capacity, leaf stomatal conductance, leaf dark respiration, bole respiration, leaf nitrogen pool, leaf nitrogen concentration, pre-dawn water potential.
- Structure and biomass: wood biomass, standing leaf biomass, wood increment, annual fine roots production, annual leaf litter production, litter leaf C/N, specific leaf weight, leaf area index, canopy height, trees age, trees density, species composition, species phenology.
- Soil physics and chemistry: soil profile description, total soil
carbon, total soil nitrogen, soil bulk density, pH, retention curve field
Harwood Forest is also one of the core CHRIS PROBA sites where work is currently carried on for developing a method for the inversion of canopy reflectance models using multi-angular hyperspectral data from CHRIS. By analysing the imagery collected over the site, it is clear that the PRI signal shows a strong angular variation with a peak near nadir and decreasing PRI with decreasing view angle. Further measurements will be carried out later this year to improve the estimation of Gross Primary Productivity from satellite data.
Current work at the site (2005)
During 2005 the flux tower will be further equipped with NDVI and PRI sensors in order to provide continuous spectral measurements. NDVI is the normalized difference vegetation index showing density of plant growth while the PRI is the photochemical reflectance index showing the light use efficiency at leaf level that can then be used to calculate Gross Primary Productivity in the canopy.
Internet links for further information
Key contacts for the Harwood Forest test site
Dr. Mathias Disney, Department of Geography and NERC Centre for Terrestrial Carbon Dynamics, University College London.
Dr Caroline Nichol, School
of GeoSciences, University of Edinburgh.
Some publications based on research at Harwood Forest
Lewis, P. E., Disney, M. I., Quaife, T., Nichol, C. and Rebelo, L. (2005) Centre for Terrestrial Carbon Dynamics CHRIS-PROBA activities: biophysical parameter retrieval from CHRIS-PROBA data over Harwood Forest, in Proc. 3rd ESA CHRIS/Proba Workshop, 21-23 March, ESRIN, Frascati, Italy (ESA SP-593, June 2005).
Disney, M. I., Lewis, P., Quaife, T and Nichol, C. (2005) A simple nested analytical model of canopy single scattering albedo, forthcoming in Proc. of 9th International Symposium of Physical Measurements and Signatures in Remote Sensing at Beijing, Oct. 17-19, 2005 (ISPMSRS05).