9. Gridded data and geographical coordinates

Aims and objectives

This lesson demonstrates the necessity of using a common geographical grid such as latitude and longitude when working with data obtained by different methods or at different times. By the end of the lesson you should be able to

• change image coordinates from [x,y] to [lon,lat],
• understand what is meant by geocorrection and why it is necessary
• resample Envisat scenes to a standard lat/lon grid,
• find the pixel corresponding to a specified geographical position,
• open a geo-referenced image based on the grid of another image,
• create a gridded composite from individual Envisat scenes
• understand the need to balance temporal and spatial resolution in gridded composites.

Section Content

1. From X and Y to longitude and latitude
2. Selecting areas with known location
3. Rectification of Envisat scenes
4. Image Registration
5. Adding coastlines and country borders
6. Creating a gridded composite
7. Summary and conclusions

Images used in this section

The data you need for this section are stored in the folder called 'tutorial_images'. Links on the left sidebar lead to more information about them. For this section of the tutorial you will use the following images:

• S19980332004040 L3M_WC_CHLO.HDF
  Weekly chlorophyll-a climatology for the 8-day period 2 - 9 Feb based on 6 years of SeaWiFS measurements from 1998 to 2004.
• MER_RR_2COLRA200402*.N1
  Three Level 2 scenes from the MERIS sensor on Envisat, showing the Benguela upwelling area in early February 2004.
• USGS_10S8E_40S30E.DAT
  USGS Coastline map of the Benguela region off the coast of south western Africa.