FAQ
About the VGT products
- What are the different VEGETATION products?
- The standard VEGETATION products are:
* VGT-P products (physical values)
* VGT-S1 products (daily MVC synthesis)
* VGT-S10 products (ten-day MVC synthesis, also in degraded resolution)
* VGT-D10 products (ten-day BDC synthesis, also in degraded resolution)
Three ten-day syntheses are made during a month:
* synthesis from the 1st to the 10th of the current month
* synthesis from the 11th to the 20th of the current month synthesis from the 21st to the end of the current month - What are VGT-P products?
- VGT-P (P= physical) products are adapted for scientific applications requiring highly accurate physical measurements. The data is corrected for system errors (error registration of the different channels, calibration of all the detectors along the line-array detectors for each spectral band) and resampled to predefined geographic projections chosen by the user. The pixel brightness count is the ground area's apparent reflectance as seen at the top of atmosphere (TOA). Auxiliary data supplied with the products allow users to process the original reflectance values using their own algorithms.
Each pixel in the image represents a ground area of approximately 1km x 1 km. The image products cover all or a part of a VEGETATION segment (data strip over land). - What are VGT-S products?
- VGT-S (S= synthesis) products are MVC or Maximum Value Composite Syntheses. The pixels selected for the syntheses are based on the selection of the maximum NDVI value, to ensure coverage of all landmasses worldwide with a minimum effect of cloud cover. The pixel brightness count is the ground area's reflectance (corrected for atmospheric effects); pixels in the sea area are set to 0. A map of computed normalised difference vegetation index values (NDVI image plane) is also supplied with the product.
Each pixel of a VGT-S product represents a ground area of approximately 1 km x 1 km. The global coverage of a synthesis extends from 75°N to 56°S. A VGT-S product can be ordered as a VGT-S1 or a VGT-S10 product, in a map projection specified by the user, covering the whole world or a selected part (region of interest) defined by the user. - What are VGT-S1 products?
- VGT-S1 products (daily synthesis) are composed of the 'best' ground reflectance measurements of all segments received during one day for the entire surface of the Earth. This is done for each of the images covering the same geographical area. The areas distant from the equator have more overlapping parts so the choice for the best pixel will be out of more data. These products provide data from all spectral bands, the NDVI and auxiliary data on image acquisition parameters.
- What are VGT-S10 products?
- VGT-S10 products (ten day synthesis) are compiled by merging segments (data strips) acquired in a ten days. All the segments of this period are compared again pixel by pixel to pick out the 'best' ground reflectance values. These products provide data from all spectral bands, the NDVI and auxiliary data on image acquisition parameters.
A MVC synthesis can be delivered with several spatial resolution (1*1 km2 or 4*4 km2 or 8*8 km2). Those three products are called:
* S10 for 1*1 km2
* S10.4 for 4*4 km2
* S10.8 for 8*8 km - What are VGT-D10 products?
- VGT D-10 products are BDC syntheses or BiDirectional Composite syntheses. These syntheses are based on a bidirectional reflectance distribution function.
The pixel brightness count is the ground area's reflectance; pixels in the sea area are set to 0.
A VGT-D product covers the whole world or a selected part (region of interest) and can be ordered in a map projection specified by the user. The global coverage of a synthesis extends from 75°N to 56°S. A map of computed normalised difference vegetation index values (NDVI image plane) is also supplied with the product.
A BDC synthesis can be delivered with several spatial resolution (1*1 km2 or 4*4 km2 or 8*8 km2). Those three products are called:
* D10 for 1*1 km2
* D10.4 for 4*4 km2
* D10.8 for 8*8 km2
Reference: Duchemin, B., Maisongrande, P., Dedieu, G ., Leroy, M., Roujean, J .L., Bicheron, P., Hautecoeur, O., Lacaze, R., 2000. A 10-days compositing method accounting for bidirectional effects. Proceedings of the VEGETATION 2000, Belgirate Italy (3 - 6 April 2000): 313 - 318.
Papers and a CD-rom of the Vegetation 2000 conference can be obtained by sending a mail to iuc.vegetation@jrc.it. - In which projections can I order VEGETATION products?
- Since no cartographic projection retains its geometric qualities globally, a specific cartographic projection should only be used for the region where the major part of its qualities is best preserved. It is important to avoid using a cartographic projection in a region for which the projection is not designed. It is also advisable not to use a projection in a region with large geometric distortions (surface or angles).
The following table enumerates the available projections for VEGETATION products.
Projection Name
Class
Best quality
Do not use
Plate Carrée
Global
Equator
Poles
Goode Homolosine
Global
Equator
Poles
Sinusoidal Equal Area
Global
Equator
Poles and 180° meridian
Mercator Equatorial
Global
Equator
Poles
UTM
Regional
Central Meridian
Away from the central meridian
Lambert Europe
Regional
Europe
Outside Europe
Albers US
Regional
North America
Outside North America
Stereo polar North
Regional
North Pole
Equator
Stereo polar South
Regional
South Pole
Equator
Stereo locale
Local
Tangential point
Far from the tangential point
- What are the different planes in the VEGETATION product?
-
Plane
Description of the plane
File format
Type of product
PHYS_VOL
Physical Volume descriptor
Information about the delivery
TXT
P/S/D
LOG
Logical Volume descriptor
Information about
- the product
- map projection information (general information, geodetic system parameters, projection parameters)
- cartographic location
- geographic location
- image co-ordinates (corresponding to carto and geographic location)
- geometric correction
- radiometric correction
- orbit parameters
- date and time
- algorithms references
- productionTXT
P/S/D
RIG
Copyright Descriptor
Information about the copyright
TXT
P/S/D
BO
B0 spectral band
Radiometry data
HDF
P/S/D
B2
B2 spectral band
Radiometry data
HDF
P/S/D
B3
B3 spectral band
Radiometry data
HDF
P/S/D
MIR
MIR spectral band
Radiometry data
HDF
P/S/D
NDV
Vegetation Global Index
NDVI indices
HDF
S/D
SM
Status Map
Data about
Bit NR 7: Radiometric quality for B0 coded as 0 if bad and 1 if good
Bit NR 6: Radiometric quality for B2 coded as 0 if bad and 1 if good
Bit NR 5: Radiometric quality for B3 coded as 0 if bad and 1 if good
Bit NR 4: Radiometric quality for MIR coded as 0 if bad and 1 if good
Bit NR 3: land code 1 or water code 0
Bit NR 2: ice/snow code 1 , code 0 if there is no ice/snowHDF
P/S
Bit NR 1:
0
0
1
1
Bit NR 0:
0
1
0
1
clear
shadow
uncertain
cloud
BSM
BDC Status Map
Data about
Bit NR 7: BRDF model adjustment quality on B0: coded as 0 if bad quality and 1 if good
Bit NR 6: BRDF model adjustment quality on B2: coded as 0 if bad quality and 1 if goodBit NR 5: BRDF model adjustment quality on B3: coded as 0 if bad quality and 1 if good
Bit NR 4: BRDF model adjustment quality on MIR: coded as 0 if bad quality and 1 if good
Bit NR 3: land/water: coded as 1 if land and 0 if sea
Bit NR 2: ice/snow: coded as 1 if there is ice/snow and 0 if notBit NR 1: cloud/shadow or clear: coded as 1 if there is cloud/shadow and 0 if not
Bit NR 0: qrmir: Radiometric quality for MIR coded as 0 if bad and 1 if good
HDF
D
VZA
Viewing zenith angle grid
Data of the satellite zenith angles
HDF
P/S
VAA
Viewing azimuth angle grid
Data of the satellite azimuth angles
HDF
P/S
SZA
Solar zenith angle grid
Data of the solar zenith angles
HDF
P/S
SAA
Solar azimuth angle grid
Data of the solar azimuth angles
HDF
P/S
WVG
Water Vapour grid
Data of water vapour
HDF
P
OG
Ozone grid
Data of ozone
HDF
P
AG
Tropospheric Aerosol grid
Data of aerosols
HDF
P
1BL
1B HRVIR latitude plane
Data of the HRVIR co-location (latitude)
HDF
P
1BO
1B HRVIR longitude plane
Data of the HRVIR co-location (longitude)
HDF
P
TG
Time grid
Each pixel is expressed with a precision of one minute referring to the beginning of the first segment of the synthesis.
HDF
S
SZN
SZ NORM
This value is the normalized solar zenith angle used in the BDC correction.
HDF
D
TP
TAUP: Optical thickness
This value is the average of the optical thickness of the selected measures of the BDC period.
HDF
D
Kxx
K0, K1, K2 for the the bands B0, B2, B3 and MIR
These values are the coefficients of the BDC correction function.
HDF
D
QL
Quick look
Quick look of one spectral band (see LOG file which spectral band)
TIF
P/S/D
P= VGT-P product
S= VGT-S product
D= VGT-D product
TXT= text
HDF= Hierarchical Data Format
TIF= TIFF Format - What is the Physical Volume descriptor?
- The Physical Volume descriptor (Phys_vol.txt) is a leader file of a support or ftp file, containing some basic infromation and the list of files available in the product. This file is also usefull when the product is split on serveral supports.
- What is the Logical Volume descriptor?
- The Logical Volume descriptor contains information about the product, map projection, cartographic en geographic location, image coordinates, geometric and radiometric correction, orbit parameters, date and time, algorithms references and production.
- What is the relation between the digital number and the real VEGETATION reflectance value?
-
The physical values of VEGETATION data can be calculated by the following formula:
Real reflectance value VGT =coefficient a * Digital Number + coefficient b = a * DN +b Coefficient a = 0.0005 Coefficient b = 0.0 - What is the relation between the digital number and the Physical Volume descriptor?
- The Physical Volume descriptor (Phys_vol.txt) is a leader file of a support or ftp file, containing some basic infromation and the list of files available in the product. This file is also usefull when the product is split on serveral supports.
About VGT syntheses
- What is the difference between S10 and D10 synthesis?
-
BDC syntheses differ from MVC syntheses in the following aspects:
* The status map of an BDC synthesis includes the following indicators: sea/land, ice-snow/not ice-snow, clouds or shadow/clear, MIR quality, BRDF model adjustment quality flag for each band.
* The following new planes are added: SzNorm, TauP and for each spectral band: K0, K1, K2.
* The following planes are dropped: viewing angles, solar angles, time grid. - What is the Goode Homolosine projection?
-
Figure : The 12 zones of the "Interrupted Goode Homolosine" projection: 2 zones northwards of 45°N, 6 in the equatorial belt, and 4 southwards of 45°S.
The Goode Homolosine projection is often used for global data sets. In fact, this projection is made of two different projections: in the equatorial belt the Goode Homolosine projection uses the sinusoidal projection, while in the polar regions the Mollweide projection is adopted. One of the main advantages of this projection is its equivalency. To avoid the large distortions, typical for the family of equivalent projections, the Goode Homolosine projection divides the globe in 12 longitudinal zones. As one can see in the figure, the margins of these zones are often situated in the oceans. Hence, all the large continents are constituted of a few neighbouring zones. Antarctica and Greenland are the only exceptions to this rule. Each zone is projected separately around a central meridian what causes only small distortions on the continental scale. A result of this method is that between some zones there are large gaps that do not correspond to physical parts of the globe.
About the VGT instrument
- What are the characteristics of the instrument?
- * Spatial resolution: in both directions 1.15 km at nadir;
* A continuous and global monitoring of the continental areas either through the centralised archiving and processing facility, or, for local or regional studies;
* Long term data sets with accurate calibration and positioning, continuity and consistency through the renewal of the system with further satellites;
* High quality related to the radiometric and geometric characteristics;
* Operate with a frequency of acquisition adequate for following changes in the vegetation cover (growth cycle, season,...) over all land surfaces of the earth;
* It uses the push-broom technology so the images will present much less geometric distortions (it will be easier to superimpose images taken at different dates and a larger proportion of the orbital strip will be useful);
* Multi-scale approaches of surface parameters and processes using simultaneous measurements acquired through the VEGETATION instrument and the High Resolution instrument on the same SPOT4 platform;
* Local receiving stations will make VEGETATION data directly available to the local users. - What are the specific characteristics of the VEGETATION images?
- The next table gives an overview of the VEGETATION spectral bands, developed specific for monitoring vegetation conditions:
Spectral band
Wavelength
B0 (Blue)
0.43 - 0.47 µm
B2 (Red)
0.61 - 0.68 µm
B3 (NIR)
0.78 - 0.89 µm
MIR (SWIR)
1.58 - 1.75 µm
About the VGT entity
- Who are the VEGETATION product distributors?
- VEGETATION products are distributed from 1st January 2007 onwards by VITO (worldwide distribution) and by the distribution partner SPOT Image (L-Band Station).
Contact Spot Image
Patrice Galey
Tel : +33 562 19 43 36
Fax : +33 562 19 40 51
Contact VITO
Tel : +32 14 33 68 77
Fax : +32 14 32 27 95 - How can I order VEGETATION products?
- VEGETATION products can be ordered on the Internet through the VEGETATION Catalogue. The catalogue is freely accessible for browsing, but for ordering you should be registered. To register, you should contact VITO.
The products can be ordered:
* by catalogue: for images in the catalogue
* by subscription: for images over a future period (a few weeks to several years) covering a particular region of interest
The following order information is needed for both orders:
* Region of interest (ROI)
* Period
* Product type (P, S1, S10, S10.4, S10.8, D10, D10.4, D10.8)
* Projection
* Delivery media - What are the delivery supports?
- There are 3 kind of supports for delivery of VEGETATION products:
* FTP (products are compressed by default in ZIP format)
* CD-ROM
* Tapes : DAT (2Gb 90 m format DDS1) - DLT (40Gb Compact Tape IV with hardware compression)
The supports (CD-ROM, DAT and DLT) are dispatched to the user.
The products by FTP are obtained from the FTP server at the Vegetation Image Processing Centre (CTIV). The user receives an e-mail with the information when a product is ready. However, if the user does not retrieve the product after 10 days the product will be automatically copied onto CD-ROM and mailed to the user.
About VGT1 <-> VGT2
- What if I have special dietary needs? (due to allergies or religious restrictions)
- This is the answer
- Where can I spend my meal plan allowance?
- Answer here
- What happens if I have money left over at the end of the term?
- This is the answer.