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,...)