9.7 Gridded data: Summary and conclusions

Now that you have worked through the Bilko tutorial section on gridded data, you should be able to carry out your own rectification and resampling of images, linking these to a standard geographical coordinate system. Mastering these techniques allow you to co-register images for direct comparison, whether digitally or by eye. It also enables you to create images that show the geographical location of a study area by locating thumbnails of your images on a larger map.

You should also be able to create gridded composites of more than one image, whether these are from the same sensor over a period of time, or from several sensors on different platforms that all measure the same geophysical parameter. Although there are a large number of gridded images available on the Internet, these do not always use the temporal or spatial resolution you may require. Nor do they necessarily cover your particular area or period of interest. Being able to create your own 'Level 3' data may therefore be quite useful.

Whenever you carry out this type of work you should consider a number of issues that we have touched on in this part of the introductory tutorial:

• How to balance temporal and spatial resolution to provide optimal data for the purpose of your study.

• The need to exclude data of doubtful validity without using selection criteria that are too stringent to give you enough data points.

• The potential errors in your composites, whether these are
  • geographical (arising from original errors in geo-referencing as well as from the process of rectification and resampling),
  • due to data selection (arising from missing data, or from including data points of a lower than usual standard),
  • or due to combining sources that may not be directly comparable (data from sensors with different characteristics or derived using different processing algorithms).

Any details of the Bilko software on coordinate systems, rectification and resampling that has not been covered in the previous subsections, can be picked up from increased experience with Bilko and the handling of different types of image data. If you are uncertain about the function of a particular software feature, reference to the the context sensitive help system will help you - just point the cursor and press F1.