Dear Esmaeil,

Certainly the Landsat imagery, which has images even older than 40 years. If the drought problem is local, I suggest asking the local authority that is responsible for photogrammetric data in your country if they have images from flight campaings.

Below is a search engine for Landsat images.

https://earthexplorer.usgs.gov/

Best regards,

Maciej Lisiewicz

Try NOAA Earth Satellite Service, Maryland, USA. Bill Pichel used to be in charge.

Dear Maciej,

thank you. All the sources I have reviewed have seldom relied on Landsat images at the provincial level because of their low temporal resolution in drought applications. Do you think the combination of Madis and AVHRR images is not appropriate? By using a regression relationship of their two years in common and building their relationship.

Dear Sandy,

Thank you very much. In your opinion, the images of this satellite, since they have a very low spatial resolution (about 10 km and Modis half a kilometer), will have a good estimation accuracy in monitoring drought in very dry areas. And given the two-year joint course of Modis and AVHRR, what do you think of the relationship between them by regression communication?@Sandy Bartle