1186 
The data are coded on 10 bits. The reflectance values are coded on 1000 levels with 0.001 resolution. The 
spectral radiance in band 3 is multiplied by 100. The brightness temperature are coded from 0 to 1023 
representing respectively 223 K and 323.3 K with 0.1 K resolution. The SST is coded from 0 to 500 representing 
0 C to 50 C. The NDVI is multiplied by 1000. 
5 The Data Visibility 
Based cm past experience the data visibility is assured through an inventory (also called Catalogue) which is a 
hi gh level description of the archived data products and a Browse products data set (generally a set of Quick 
Looks). The way of physically viewing the data products is done through printed Quick Lode inspection, CD- 
ROM collection or network access. The useful tool to manipulate the Quick Look data set is “called” Browser. 
The Figure 3 s umm arize the different mode to evaluate the data before ordering products. 
5.1 Central Catalogue 
AVHRR data information are collected into a catalogue system maintained by ESRIN and called “LEDA” fully 
described in the LEDA Users Guide (Earthnet, 1990, Tobiss and Muirhead, 1989). LEDA makes use of the 
Inventory Exchange Format (IEF) information collected through the stations and centralised at ESRIN. For the 
description of the IEF please refer to CEOS, (1992). LEDA allows user to interrogate remotely about the 
availability of a scene entering the time and location of the request The query can refer to other types of 
information like the cloud cover per image. 
5.2 Visibility of the ESA Archive 
The concept developed for CZCS was improved for AVHRR: Quick Looks, corresponding inventory and a 
browse software were interfaced to provide to the user an easy to use service distributed on CD or accessible 
through network. 
5.2.1 The Ionia Quick Look products 
A new AVHRR Quick Lock generation algorithm has been developed in order to: 
• give a better visual impression of the image quality. 
• be valid for any NOAA satellite and independent of latitude and acquisition time (calibrated data). 
• highlight land ocean atmosphere geophysical features (e.g. cloud height, water temperature, sun glint, vegeta 
tion strength, active fire, ice and snow). 
This Quick-Look image is a 3 colour composite of channel 1 reflectance, channel 2 reflectance, channel 4 
brightness temperature. A classification into water, vegetation, bare soil, cloud has been performed on each 
channel before multiple histogram equalization. The Quick Lode is a 512x480 pixels (3x3 pixels average) image 
coded on 8 bits representative of the SHARP image product. Furthermore the red pixels mark the active fire 
detected by the Quick-Look algorithm, (Aiino et al„ 1993). 
This Quick Look extends the standard geographical and cloud cover information to additional qualitative but 
also to quantitative information on the features that appears in the higher level application products (e.g. land 
monitoring, oceanography, biomass burning, clouds statistic and physique,...)