Description of NOAA-AVHRR image archive at KNMI

1. Introduction

The use of meteorological satellites for the observation and monitoring of processes at the Earth surface is widely perceived around the world. Since 1981 KNMI is operating an HRPT receiving station (the only one in the Netherlands) for NOAA satellite data. Starting in 1985 KNMI is researching and developing products and applications of NOAA/AVHRR image-data of land and sea surfaces. Many users of those products are served by KNMI in the past. An extensive NOAA/AVHRR image archive has been built up at KNMI.

The HRPT receiving station at KNMI is the main source for the feeding of the KNMI NOAA/AVHRR land/sea image archive. The following NOAA/AVHRR image products of The Netherlands, the North Sea and Europe are generated on a routine basis:

Selected images are archived (based on the amount of cloud cover). Weekly composite maps of SST, Reflectance and NDVI are generated every Monday and archived. Single channel (1 until 5) images of the Netherlands are generated routinely and stored on-line for one week. For certain periods NOAA/AVHRR image products of certain areas within the field of view of the HRPT-antenna of KNMI are generated on request of certain users. Those image products are also stored in the archive.

For use in retrospective studies KNMI has obtained raw NOAA/AVHRR data of more than 700 NOAA-passes from the NERC Satellite Data Archive at the University of Dundee. Most of the Dundee data is processed towards value-added image products (as listed above), which are put in the archive.

The metadata of all routinely produced and archived NOAA images of the North Sea and The Netherlands are included in a Dbase-file NOAALIST.DBF (the current size is about 1 Mb). The Dbase-file contains over 13.000 entries covering the period from January 1990 until now. The Dbase-file can be imported in MS-Excel too. For a description of the metadata fields in the Dbase-file click here.

A paper on the now 10-year KNMI archive of NOAA-AVHRR SST images of the North Sea was presented at the 1999 EUMETSAT Conference in Copenhagen (click here to read the paper).

2. Owner

The owner of the NOAA/AVHRR archive is KNMI.

3. Maintenance

The NOAA/AVHRR archive is maintained by Hans Roozekrans.

4. Platform

The satellite images are processed on a DEC/Alpha system (node BDASAT) under OpenVMS.
The image files are archived on MS-DOS formatted WORM-discs.

5. Dissemination regulations

The images in the archive are freely available for users within KNMI.
For users outside KNMI image products are available according to the conditions described in the KNMI Product Catalogue (text is in Dutch).

6. Protection

The archive is not public accessible. To obtain image files contact the archive-manager (E-mail: Hans Roozekrans).

7. Dimensions

The standard North Sea (50 - 60 °NL) and Netherlands image products are continuously archived at full 1-km resolution since January 1990 until now. More than 13.000 images are archived until now.

Weekly SST and NDVI composites of images at 2-km resolution covering resp. all European waters and a large part of the North Atlantic Ocean and the whole of Europe are archived since August 1995 (meta data of this part of the archive are not included in the Dbase meta database).

The archive also contains irregular NOAA/AVHRR image products at full 1-km resolution of the following areas: Turkey, Greece, Spain, Italy, Iceland, Ireland. Monthly NDVI-images of all Europe for 1993 are archived.

The complete "WORM" image-product archive contains about 10 Gb.

The "Dundee" part of the archive is very irregular concerning the areas (within Europe and northern Africa) and dates (within the period 1982 until now) of the images.

8. Description

8.1 File names
The filenames of NOAA/AVHRR images in the archive start with a character, most of the time connected with the area of coverage (i.e. N: North Sea, Y: IJsselmeer etc.). The rest of the name contains information on the date and time of the image. The extension directs to the parameter type of the image (SST: Sea Surface Temp., NVI: NDVI, REF: Reflectance etc.).

8.2 Data format
All image files are stored in the so-called NOAAPC format, which is an in-house developed easy to read binary format. A description of the format can be obtained from the archive managers.

9. Utilities

KNMI has developed a software package NOAAPC, running on MS-DOS/Windows systems with EGA or VGA adapter, to display and manipulate the image files. Options are available within NOAAPC to convert the "KNMI" image files to ARC/Info and ERDAS GIS files. NOAAPC is public domain software and can be obtained from the archive managers.

10. Storage time

The image files in the WORM archive will be stored indefinitely. Real-time image files of all NOAA-passes are stored during one week on the DEC Alpha system.



Back to archive description

Description of Dbase-file of the KNMI NOAA-AVHRR image archive

1. Introduction

All NOAA-AVHRR image files of the North Sea, archived on WORM optical discs at KNMI since January 1990, are described in a Dbase-file called NOAALIST.DBF (the current size is about 1 Mb). The file is weekly updated. The file can also be imported in MS-Excel.

All images in the database contain higher level data (e.g. Sea Surface Temperature, Vegetation Index etc.) and are polar stereographic projected. Most image-files in the database are generated by the on-line production system for the North Sea area. Some are generated on ad-hoc basis for specific projects in several areas in Europe.

The Dbase-file is currently maintained in a Windows environment. Although the PC is connected to the KNMI-network and thus the Internet the database is not on-line accessible from outside.

2. Structure of Dbase-file

The Dbase-file is record structured. For every archived image-file one record is used. Each record consists of 22 fields with information on the image:

1 NOAAFILE (12 chars.):

The name of the image-file.


The first character of the filename indicates to the area of the image:
K = complete North Sea (between 60 and 49 degr. North)
N = southern North Sea (between 55.3 and 50 degr. North)
Y = IJssellake (located inside The Netherlands)

The positions 2 until 8:


NW = weekly composite of the North Sea; the positions 4 and 5 indicate to the week number; 6 and 7 to the year; an N at position 8 indicates to a "night" composite (composed of only nighttime images)
A number at 2 until 8 indicates to an instantaneous image and holds the date and time of the image

The filename extension indicates to the parameter of the image:


SST = Sea Surface Temperature;
REF = Reflectance;
TSM = Total Suspended Matter;
NVI = Vegetation Index;
IJS = Ice cover.

2 CREATOR (1 char.):

Indicates the origin of the data:

K = data received at KNMI
D = data received at Dundee station.

3 YEAR (2 digits):

Year of observation of satellite image.

4 MONTH (2 digits):

Month of obs. of sat. image.

5 DAY (2 digits):

Day of obs. of sat. image.

6 HOUR (2 digits):

Hour of obs. of sat. image.

7 MINUTE (2 digits):

Minute of obs. of sat. image.

8 SATNUMBER (2 digits):

ID of NOAA-satellite (e.g. 11 = NOAA 11)

9 ORBIT (5 digits):

Number of NOAA-orbit.

10 MINLAT (5 digits):

The latitude (in decimal degrees) of the bottom right corner of the image.

11 MAXLAT (5 digits):

The latitude of the upper left corner.

12 MINLON (6 digits):

The longitude (in decimal degrees) of the upper left corner (negative means West; positive means East).

13 MAXLON (6 digits):

The longitude of the bottom right corner.

14 USEDIMAGES (2 digits):

If the number is 1 this indicates that the image is an instantaneous or single-pass image. If the number is larger than 1 the image is a composite of 2 or more instantaneous images (e.g. a weekly composite). The number indicates the amount of images used for the composite.

15 CLOUDFREE1 (3 digits):

The percentage of cloudfree pixels in area 1 in the North Sea (the North Sea is divided into 7 areas; for a map of the geography see below).

16 CLOUDFREE2 (3 digits):

Same but now for area 2.

.

.

21 CLOUDFREE7 (3 digits):

Same but for area 7 (which is IJssellake).

22 CLOUDFREE (3 digits):

The percentage of cloudfree pixels in the whole image.

 

Coverage of images with NW corner at 60° N
and 3° W. The numbers are related to the
"CLOUDFREE" fields in the Dbase-file.