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2006 Field Campaign
In June 2006 the NERC-funded Network for Calibration and Validation of EO data (NCAVEO) organised a Field Campaign in north Hampshire involving over 50 people from 22 organisations (click for list). The initial plan was to base the experiment at the Barton Bendish test site in East Anglia, but the absence of on-site instrumentation coupled with uncertainty about access to this site and its distance from the main research groups led to a search for other suitable sites. The one chosen was centred on the Services and Technology Facilities Council Chilbolton Facility for Atmospheric and Radio Research (CFARR), approximately 45 km north of Southampton (Figure 1). CFARR comprises a number of state-of-the-art instruments for measuring atmospheric properties, including the 25 metre diameter Chilbolton dish, a 3 GHz doppler-polarisation radar, 1275 MHz clear air radar and a UV vertical sounding LiDAR In addition, the site has a full suite of continuously operating meteorological instruments.
Description of the site
The CFARR facility is located on a plateau above the floodplain of the River Test, on an area formerly used as a military airfield. Little evidence of the airfield remains except for a few buildings currently used as agricultural storehouses and parts of the former concrete runways and associated aprons.
The area around the research station is mainly agricultural fields which in June 2006 were growing barley, wheat, oats and oilseed rape or left fallow. Harewood Forest, north of the River Test comprises conifer plantations and areas of broadleaf woodland, and is criss-crossed with access tracks, a legacy of its former use as an area to store munitions. Large parts of the floodplain of the River Test were formerly managed as water meadows, a traditional method of grassland management in which parcels of land were seasonally flooded by water flowing thorough a system of diversionary channels and sluices.
Two areas of semi-natural wet grassland remain, Chilbolton Cow Common and Bransbury Common, the latter having protected status as a site of special scientific interest (SSSI). The total extent of the study area was 9 km north-south by 6 km east-west, the south-west corner being defined by Ordnance Survey grid reference SU370360.
Planning the experiment
Planning for the experiment began in December 2005, and once the necessary permissions from landowners had been secured, a land cover map of the area was prepared based on farm plans and field survey (Figure 2). An announcment was made to invite participation from the remote sensing community and a meeting was held in April 2006 to plan the experiment. This was attended by over 30 people, including Frédéric Baret, representing the VALERI project, and decided on three main aims for the experiment:
- To gain experience in the collection and use of field data to validate radiance and reflectance products from airborne and satellite sensors;
- To share best practice on the validation of leaf-area index (LAI) estimates derived from satellite sensor data;
- To assemble a quality controlled, multi-scale, multi-sensor data set for algorithm development and testing.
A window of three weeks in June was identified as the optimum period for the experiment, taking into account knowledge of the crop calendar, the probability of good weather and the availability of staff, aircraft and ground instruments. Within this three-week window, the overpass dates of the satellites involved defined several days when all participants were asked to be on standby for simultaneous field data collection. Arrangements were made to accommodate those scientists not local to the area in the village of Stockbridge, a few kilometres from the field site. Most visiting scientists stayed for 2- 3 days during the actual experiment.
A reconniassance visit was arranged for 12th May 2006, and this was very important in identifying those sites to be measured on the ground, and to discuss the method of sampling. These decisions were informed by aerial photography of the area provided by UK Perspectives, a joint venture between BlueSky International Ltd and Infoterra Ltd, one of the partners in the NCAVEO network. Following this meeting several rectangular plots were marked out with coloured flags in each of the fields to be sampled, and a GPS survey of the field sites was undertaken in advance of the main campaign.
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