looping through two sets of data

I have two sets of data, one for radar, one for lidar. The files are in csv, and i have added the data to empty lists called radar and lidar. The data is 600x600. Each row of data is in a list. so 600 values per row (and therefore per list). The radar file tells me where the islands of land are in the sea, so any values >150 will be land The lidar will tell me the height of the land. so first i used this code:

for i in range(len(radar)):
    for j in range(len(radar[i])):
        if radar [i][j] > 150:
            radar [i][j] = 'land'
        else:
            radar [i][j] = 'sea'

i now need to get the height values of all the areas classified as land (or land over >100) but dont know how to check simultaneously for land and then find its value. Any ideas?