I have to classify land use land cover data for western ghats- 1,07,770 sq km area.The landsat images for the area cover 15 tiles . I have to use minimum cloud cover images . But for the same the images available at minimal cloud cover are from different dates . Can i mosaic these images of different dates (say dec1 2014 , 30 oct 2014 ) to achieve YEARLY lulc without any problem ?
The main issue with using scenes from different times of the year is seasonality / phenology of the vegetation.
The variation in spectral response of the vegetation across the year can make it difficult to create a cloud free mosaic, but if it is possible to create multiple mosaics over the year, that can certainly help improve your LULC as the phenology is very useful for classification.
One thing that you can try is a pixel-by-pixel NDVI maximum value composite, where you retain the regular bands in your image stack. This should be done on atmospherically corrected data - an option would be to use the PROVISIONAL LANDSAT 8 SURFACE REFLECTANCE PRODUCT from the Department of the Interior U.S. Geological Survey. It may not be perfect in your area due to known issues in mountainous regions, but it may be worth a shot.