change docstring

Author: jungkyoJung

python/packages/isce3/splitspectrum/splitspectrum.py

@@ -428,8 +428,8 @@ def construct_range_bandpass_kaiser_cosine(self,
         subbandwidth = np.abs(fH - fL)
         fft_size = len(frequency_range)
 
-        assert fH < np.max(frequency_range), 'High freqeuncy is expected '
-        assert fL > np.min(frequency_range), 'Low freqeuncy is lower than observation'
+        assert fH < np.max(frequency_range), 'High freqeuncy is out of freqeuncy bins'
+        assert fL > np.min(frequency_range), 'Low freqeuncy is out of freqeuncy bins'
 
         # sampling frequency is 1.2 times wider than bandwith
         sampling_bandwidth_ratio = 1.2