Contents:
1. Ordering Seawifs Data
2. Processing to Level 2

Ordering SeaWiFS Data

Ordering SeaWiFS imagery (1997-present,S***): Password required
For this class purpose, choose only a day's worth of image. After clicking find swath, a new page appears ,  with many scenes. Enter your password on the top left menu 'SeaWiFS user login'. You can download any one scene directly by subsequent clicking on the file name. If ordering more than one scenes click 'order data' (top right) , Enter your vaid email id. Click next to *Do Not* extract my order for me. Click on desired products below Level 1 / Level 2 and ancilliary products.  Click Review order and Submit order in next page.

After you have clicked away confirming your order, you will get a confirmation by e-mail from the DAAC. Reply to that (without writing anything in it, see instructions). A couple of mins/hours later (depending on the volume of data requested), or sometimes next day, you will get a 'Data Ready' e-mail with instructions where to ftp the data from. Download your data within 3 days, otherwise they might be deleted from the f tp-site. To FTP follow these instructions.

You can also download the files directly to ocean by using the command ftp or a more userfriendly version ncftp. To transfer date from your computer to  ocean  use ftp software on PCs running Windows is SecureFX, on a Mac you can use Fetch. Be sure to use binary mode ('raw data' for Mac), not ascii or text, when ftp'ing the datafiles.

Ordering SST Data

Pathfinder/AVHRR: Download from NODC-NOAA website, select Available Data. Normally you would use '1. Direct FTP Access'

MODIS:
    From the oceancolor.gsfc.nasa.gov website

SeaDAS: To find images for today's class:

Level 1 to Level 2 image processing
Level 1 files contain the radiance counts at each channel received by the SeaWiFS sensor. To translate these to normalized water leaving radiance, chlorophyll, etc. we have to process the files to Level 2 by applying atmospheric corrections and bio-optical algorithms. The SeaDAS function to do this is called: 'msl12'. This program can generate a total of 176 (!) different products. See also Overview of SeaWiFS Data Processing and Distribution on the OceanColor website. There is a similar page for MODIS-Aqua.

Select from the SeaDAS Main Menu: Process -> SeaWiFS -> msl12,0 - L1A or L1B to L2 processing. Select the L1A input file in the of  SeaDAS SeaWiFS L2 Generation Program window. It will automatically suggest the Level 2 output file name (first part of L1A file + L2_GAC extension) and start checking if the needed ancillary files are present, like meteorological and ozone data. If they are not present SeaDAS will download them for you. Then click on 'Select L2 Products' where you can make your choice of the 176 different products (see MSL12 Output File 1 L2 Products Selection Widget) . You can choose 'default' value or any more of your choice, but each processing takes time. One L2 output file can contain more then one products (similar to the 8 bands stored in the L1A-file). However, you can also spread out some specific dataproducts over different L2-output files.

You can also do some subsampling of your image using 'subset/subsample' from the SeaDAS SeaWiFS L2 Generation Program window. L1->L2 processing is very cpu intensive and can take quite some time. Therefore it is advised to select only the specific region on the image you are interested in for processing. This can be done by selecting the pixel and line range on the image or using lat/lon coordinates. 

With Ancilliary files and processing options, you can manipulate the way msl12 will calculate the L2 products. Normally you leave them as is. By default SeaDAS will not try to use near real-time data which will be downloaded automatically. You can also opt for climatological data. If you want to manipulate the processing, click on the Processing Options tab. You can also change flag thresholds.

When you are ready to do the L2 processing, click on either 'Run' or 'Run(BG)'. The difference is that with 'Run(BG)' the process will run in the background and you can still do other things in SeaDAS. With 'Run' you have to wait until it is done before you can do anything else. If you have a list of files to process running it in the background is advised.

Processing MODIS-Aqua data requires 2 extra steps. From the OceanColor website you can get L1A_LAC data containing uncalibrated radiances at 19 bands (more info).

Unlike SeaWiFS geolocation data (latitude/longitude info) is not included in the L1A file and has to be generated first. From the SeaDAS Main Menu, select: Process -> MODIS -> geolocate - L1A to GEO processing. Select your MODIS L1A input file. The output GEO file name is automatically generated. To generate the geolocation Attitude and Ephemeris files are needed. They will automatically be downloaded if not already on the server. Click on Run to start the process.

Now we are ready to create a L1B file which will contain calibrated radiances. From the SeaDAS Main Menu, select: Process -> MODIS -> modis_l1bgen - L1A to L1B processing. Select your Input L1A file.

It will automatically pick the geolocation file (GEO file) created in the previous step, and suggest output file names. Usually you only want to retain the LAC (1km) file. Click on Run. After it has finished you can select Display to see what Products have been generated.