Good afternoon, how can you do multispectral crop mapping? To understand what will be the yield, whether additional irrigation of the land or not enough water in a certain area of the field.

They used to put a specialist in a small Colt airplane and do monitoring, it was not accurate, but you could at least determine the yield. I can't tell you about irrigation and the rest.

One of my acquaintances monitors with the help of quadcopters, but to monitor one field, it takes him about 4-5 days, it is very much, because the fields are large, and quadcopters have small battery capacity.

Perhaps there are civilian UAVs that can be used to monitor businesses or, as in your case, crops. The exact cost of such UAVs, unfortunately, I can not tell you, because I am not interested in it.

You can find similar UAVs on Amazon, but such UAVs are not designed to monitor across the spectrum of agricultural fields. You have to use special UAVs for that. Consider the Menatir networked aerial monitoring system https://menatir.com/features and its capabilities. I think you will really like what has been created by this company. Their UAVs and software are specifically designed for multispectral crop mapping. So you can monitor your fields very quickly and do it regularly.