About 50 scientists attended the meeting. The first morning consisted of overview talks on Proba, on the CHRIS instrument and on the major scientific aims of the mission - land studies and aerosol studies. Most of the important discussion centred on the configuration of the mode of operation of the instrument (no. of views x no. of bands x spatial resolution), on the data acquisition schedule, and on the calibration of the instrument (radiometric, wavelength and other issues).

The afternoon consisted of break-out sessions on aerosol & cal/val studies, land studies (agriculture), forestry and water quality studies. I presented two talks in the aerosol & cal/val group ( on behalf of Grant and Mitchell) and two talks in the land group (on behalf of Cudahy and Huntington).

The second morning was used by the group leaders (Settle for aerosols & cal/val; Barnsley for land, Fletcher for forestry, for the coastal and Lavendar for the inland water group) to summarise the previous afternoon's discussions and to discuss the issues raised in the break-out groups amongst the whole group.

The meeting finished at 12:30 on 5 July. A closed session meeting was held in the afternoon for the Steering Committee to review recommendations and reconsider the data acquisition plan. PIs were not invited to attend this meeting.

Main Discussion Points

• [1] PIs were asked to complete a Data Acquisition Details pro-forma and return this to Mike Barnsley. These forms must be completed by all PIs who have responsibilities for CHRIS sites. I have done this for the Grant proposal and given the forms to Mitchell, Cudahy and Huntington for them to complete.
• [2] The data acquisition schedule will be a complex task and there are bound to be compromises and restrictions. The nominal data capture rate is 5 images per day, and this is determined largely by the availability of power on board Proba. Thus, PIs are unlikely to get all of their requested image acquisitions.
• [3] The mission lifetime is 12 months. However, it is anticipated that 4 months will be required for instrument validation, thus only 8 months of earth imaging will be available. Preliminary scheduling gives 1282 images for 282 days.
• [4] Wavelength calibration is to be done using the 760 nm Oxygen absorption feature (A-band), but other possibilities were discussed (e.g. using Fraunhofer lines or water vapour features).
• [5] Tests sites were designated in 3 categories - core sites, additional sites and reserve sites. It was hoped that some rationalisation of these sites would occur due to the paucity of data acquisitions.
• [6] Sites for calibration apparently have not been considered in detail previously. At my urging it was recommended that the images of the Libyan desert and Railroad valley be acquired for relative and absolute radiometric calibration. Some animated discussion occurred about the utility of the Libyan desert site as its BRDF is not measured and there was some uncertainty concerning the uniformity of the site at 25 m resolution. Discussion ensued concerning using other satellite instruments to calibrate CHRIS by imaging the same sites and by imaging the Greenland ice-sheet, the Antarctic plateau or high, dense clouds.
• [7] Several band configurations were suggested by various PIs and all PIs were encouraged to think about band selections carefully. PIs were discouraged to suggest too many variants as this would complicate the programming of the instrument. I suggested that all band configurations should include a water vapour band (936 nm) and aerosol bands for atmospheric correction. Wavelength calibration will be done only a few images and the analyses will be used to correlate the results with the detector temperature. The detector temperature will then be used on all other images to characterise the wavelength shifts.
• [8] The pointing accuracy of the instrument was quoted as 0.1 degrees resulting in a pixel location accuracy of ±2 km and satellite positional errors were thought to be of similar accuracy. Collocation of the images and absolute navigational accuracy were issues common to all proposals and these are being addressed.
• [9] Mike Barnsley has agreed to set up four electronic discussion fora for the mission. The topics will be:- (a) General, (b) Land applications, (c) Aerosols, and (d) Coastal and Inland Water. PIs will be informed by email about the address details of the sites.
• [10] There were uncertainties in knowing the precise number of days required by the mission operators for data acquisition programming. Some thought has been given to using weather forecast information to schedule CHRIS image acquisitions.
• [11] Details of the mission and updates can be found at: www.chris-proba.org.uk

Fred Prata

6 July, 2000.