How can I calculate circles area's in polar graph

I have a polar graph like that https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSwGrrHSNbsRX3IHnHgptob9n8USFHFQgwxUKS71tCUo3XonkIb and there is 2 circles that i want to calculate their area’s. Is there any way to do this? My last option is using openCV to calculate from image. Thanks lot…