Frequently Asked Questions (FAQ)

Categories:

GENERAL
 
Why was this project started?
 
Who is involved in the Project?
DATA
 
What is the dataset comprised of?
 
Where can I get data from?
 
Where is the most recent data kept?
 
What composites periods are available?
GOODES
 
Why use the Goodes projection?
 
How do I convert from the Goodes projection to another?

GENERAL

Why was this project started?

Scientific investigations initiated in the late 1980s, indicated that global change information could be derived from the 1-kilometer advanced very high resolution radiometer (AVHRR) data acquired by the National Oceanic and Atmospheric Administration's (NOAA) Television Infrared Observation Satellite (TIROS). Over the intervening years various scientific organizations have identified the need for compiling a global 1-km resolution multi-temporal AVHRR data set.

Who is involved in the Project?

There are four major participants in this project, namely NOAA, with its High Resolution Picture Transmission (HRPT) stations and the Local Area Coverage (LAC) recorder; ESA, with its AVHRR HRPT ground station network; and the USGS and NASA, with the USGS/EDC AVHRR HRPT ground station network augmented by key CSIRO/Australian HRPT stations, cooperate to assume responsibility for the acquisition and compilation of a global land 1-km AVHRR data set.

Over 30 AVHRR receiving stations involving over 32 organizations in 20 countries cooperate to acquire, archive, process, and distribute the project's data. It is important to note, that without all of those stations' and organizations' support, this project could not be accomplished. A list of the partners can be viewed by following this link .

DATA

What is the dataset comprised of?

The data set is made up of 5-channel, 10-bit, raw AVHRR data, at 1.1-km resolution (at nadir) from each daily afternoon pass over all land and coastal zones using data from NOAA's polar-orbiting TIROS. Initially the data were to be collected continuously for 18 consecutive months beginning April 1, 1992, and continuing through September 30, 1993, subsequently the period has been extended to September 30, 1998.

Composited in 10-day increments, each 10-day record includes the following bands or channels:




      ________________________________________________________________



        Band       Description          Band      Description     



  ________________________________________________________________



       1        AVHRR channel 1          6        NDVI



       2        AVHRR channel 2          7        Satellite zenith



       3        AVHRR channel 3          8        Solar zenith    



       4        AVHRR channel 4          9        Relative azimuth



       5        AVHRR channel 5         10        Date Index



  ________________________________________________________________



    

In addition to the composited data detailed above, stitched half-orbital data in NOAA's raw, level 1b format are also available for downloading.

Where can I get data from?

Multiple data access points are being established to facilitate internet download transmission speeds. Current sites include:
EDC DAAC at USGS EROS Data Center (EDC)
European Space Agency's ESRIN Server
University of Tokyo

If obtaining the data over the Internet is not feasible, global data can be requested on 8mm magnetic tapes. Contact the EDC DAAC for further information.

Where is the most recent data kept?

Occassionally, composites are re-generated to take advantage of a new technique or to fix a bug. As soon as the data are re-generated, copies are placed on the USGS/EDC server and mailed to the other data access points. Thus, the online data is the most recent.

What composites periods are available?

Currently, composite periods are available from April 1992 to December 1995. There will be a data gap period during the time that NOAA-11's orbit decayed to the point that the local overpass times were so late in the afternoon that severe sun angles were encountered which made the data scientifically questionable. Processing of NOAA-14 data has begun and the composites will be placed at all of the distribution sites when each 10-day period is completed. For the most current information, check the scroll bar "10-day composite period" listing at Composites Dates .

GOODES

Why use the Goodes projection?

Because of the increasing emphasis on global monitoring, processing remotely sensed raster image data onto global map projections has become an important issue. One class of map projections, interrupted equal-area projections, is especially useful for this purpose. The use of the Interrupted Goode Homolosine map projection for the Global Land Advanced Very High Resolution Radiometer (AVHRR) l-km project and the AVHRR Pathfinder project has produced a map that is both attractive to the viewer and useful for data analysis. This interrupted, composite, equal-area map projection uses the Sinusoidal projection for low latitudes and the Mollweide projection for high latitudes and is broken into 12 regions, each with its own central meridian. This combination of projections helps to preserve the shape of the land masses and results in a map that has less distortion than an uninterrupted global map. The use of the interrupted projection also simplifies the processing and management of larger data sets, because the data can be processed either separately in the component projections that make up the interrupted projection or directly onto the interrupted projection.

An article discussing the Goodes projection is available for further information.

How do I convert from the Goodes projection to another?

Converting from the Interrupted Goodes Homolosine projection to a geographic or Cartesian coordinate system will result in the following:
The equal-area property of the source data will be lost.
Substantial angular deformity is introduced, especially the closer one moves to the poles.
Polar features are represented with drastic distortion and anomaly.

We recommend converting the Goode's projection only into other equal-area map projections. The Lambert Azimuthal Equal Area is one such recommeded projection. If you operate UNIX ARCINFO, AML scripts can be provided to assist in the Goodes to Lambert conversion. Contact Kent Lethcoe for more information.

To convert imagery from one projection to another, you will need access to a raster projection package. Projection of the input data (Goodes) to an output projection entails the definition of the output grid structure (pixel size and pixel framing), establishing the spatial extent of the grid, and sampling of the output grid to determine the values that are assigned to the output pixels. Raster projection packages handle all of those functions but the user must supply the X-Y projection coordinates that lay out the spatial extent of the input (Goodes) image. The projection parameters that define how those X-Y values relate to latitude and longitude must also be supplied by the user. Software is available that calculates line/sample to latitude/longitude and the inverse for the Interrupted Goodes Homolosine projection.


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