diff --git a/s1denoise/sentinel1image.py b/s1denoise/sentinel1image.py
index 388911e..a0ba6e3 100644
--- a/s1denoise/sentinel1image.py
+++ b/s1denoise/sentinel1image.py
@@ -777,6 +777,7 @@ def get_raw_sigma0_full_size(self, polarization):
         cal_s0 = self.get_calibration_vectors(polarization, line, pixel)
 
         sigma0_fs = dn.astype(float)**2 / self.get_calibration_full_size(polarization, power=2)
+        sigma0_fs[dn == 0] = np.nan
 
         return sigma0_fs