Near Real-Time Data: Map and Extraction
The near real-time (NRT) map and extraction utility allows users to directly
access the NRT image support system in order to create regions and requests
for both maps (png and/or jpg formatted, mapped products) and data extraction
(HDF extracts).
Regions
The first step in the map and extraction process is to select a region.
Users may:- Choose from a list of pre-defined regions, or
- Define a new region
- The pre-defined regions are fixed, and cannot be edited by users.
- User defined regions are only usable/editable by the user who created them.
Map/Extraction Requests
Once a region is selected, a request for maps and/or data extraction needs to be defined. At this stage, the user chooses maps (png and/or jpg formatted, mapped images) and/or L1/2 HDF data extracts.
The following options may be defined for each request:
- Maps:
- Image Width: default 600 pixels
- Add a coastline: default on
- Add a graticule frame: default on
- Add lat/lon gridlines: default on
- Add a colorbar (not all products have an available colorbar): default off
- Add a label to the image containing the parent filename: default on
- Threshold: Threshold for minimum percent of valid pixels (ocean retrievals): default 5%
- Product(s)
- Chlorophyll (default)
- SST (MODIS only) (default)
- True Color
- Normalized Water-leaving Radiance
(412, 443, 490, 510, 555, and 670nm for SeaWiFS)
(412, 443, 488, 531, 551, and 667nm for MODIS)
- Aerosol Optical Thickness (at 865nm for SeaWiFS, 869nm for MODIS)
- Diffuse Attenuation at 490nm (K490)
- Angstrom (510:865nm for SeaWiFS, 531:869nm for MODIS)
- Data Format: JPEG/PNG and/or HDF
Users may opt to have JPEG/PNG images, and/or digital data (HDF) extracts of Level 1 and Level 2 files created.
Images can be sent to the user via email or placed on our anonymous FTP site for download. All HDF data will be place on an anonymous FTP site for download. Restrictions apply to SeaWiFS HDF delivery, please contact the Ocean Color Support Services Staff for more information on these restrictions.
(NOTE:The image options apply only to the JPEG/PNG format.)
Level 2 Product Image Scaling
The Level 2 product images (gif images) use
the following scalings:
- Normalized water-leaving radiances:
- pixel_val = 255 * log10(geophysical_value/0.15)
/ log10(5.0/0.15)
- Chlorophyll:
- pixel_val = (log10(geophysical_value) + 2)/0.015
- K490:
- pixel_val = (log10(geophysical_value) + 2)/0.011
- Aerosol Optical Thickness:
- pixel_val = 200 * geophysical_value
- Angstrom:
- pixel_val = 50 * (geophysical_value + 0.5)
REQUESTING IMAGE SUPPORT
You may now request real-time image support
online
YOU MUST BE AUTHORIZED TO RECEIVE SeaWiFS IMAGES
(No authorization required for MODIS-Aqua images, although registration is required)
NRT images from SeaWiFS are available only to authorized
SeaWiFS data users who have received permission
to receive real-time image support. Please
see the page on Authorized Users.
