Hi, My study covers 1981 to 2018. I need to classify Landsat images of 1981, 1991, 2001, 2011, 2018 to get land cover. I can do accuracy assessment of 2018 classification by ground truth points. but how can i measure the accuracy of 2001 or 1991 year images?
@Md Sarowar, you can use Kappa accuracy classification check to confirm the accuracy of the 1991 or 2001 images.
This is a fairly common problem in LULC mapping. It is always possible to validate a recent map, since the land cover/land use can be checked for accuracy through field visit. However, for past LULC maps, all you can do is to use the maximum trusted data source you might have at your disposal which can be checked against your past remotely sensed maps. It can either be aerial photographs, reference LULC maps, ancillary data.
A common approach people often use is sampling from Google Earth satellite images. They are free but you cannot download them, but rather just browse them. However, since Google is providing a timeline feature for free, aiming at your area of interest, you can freely access old picture and sample data for each class of interest. Lots of published papers use this approach for validation when ancillary sources/aerial photographs or reference datasets for the past years are not available, yet it has proven to be a realiable method (see http://adsabs.harvard.edu/abs/2015SPIE.9644E..1NR and ). I can direct you to a tutorial here (https://ibis.geog.ubc.ca/courses/geob373/labs/IGETT_Exercises/google_earth_for_ground_truthing.html).
Also find attached to this answer the FAO Map Accuracy Assessment and Area Estimation practical guide advocating the same method for sampling data from Google Earth for map validation, along with formulas and a link to an interesting plugin developed to this end, CollectEarth (http://www.openforis.org/tools/collect-earth.html).
Hope this helps.
We have also faced same issues but it has been resolved by using some methods as explained in the following papers.
Article Land-Use/Land-Cover Changes and Their Impact on Surface Urba...
Article Spatial Process of Surface Urban Heat Island in Rapidly Grow...
You could get historical facts from the local people. Several software perform the accuracy assessment, such as eCognition Developer.
to make difference between "vegetation" and "built up" for example you can use the value of NDVI in Qgis
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