diff --git a/hypro/AtmCorr.py b/hypro/AtmCorr.py
index 69b5fa6..9e3bfa6 100644
--- a/hypro/AtmCorr.py
+++ b/hypro/AtmCorr.py
@@ -9,9 +9,14 @@
 
 """ Functions to do atmospheric corrections. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
+
 def atm_corr_band(atm_lut_WVC, atm_lut_VIS, atm_lut_VZA, atm_lut_RAA, atm_lut,
                   wvc_image, vis_image, vza_image, raa_image, rdn_image,
                   bg_mask):
@@ -63,6 +68,7 @@ def atm_corr_band(atm_lut_WVC, atm_lut_VIS, atm_lut_VZA, atm_lut_RAA, atm_lut,
 
     return rho
 
+
 def atm_corr_image(flight_dict):
     """ Do atmospheric corrections on the whole image.
 
diff --git a/hypro/AtmLUT.py b/hypro/AtmLUT.py
index 73f9e2d..aaac812 100644
--- a/hypro/AtmLUT.py
+++ b/hypro/AtmLUT.py
@@ -9,7 +9,11 @@
 
 """ Functions to build an atmospheric lookup table (LUT). """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
 # Define atmosphere database parameters. Do not make any change to them.
@@ -23,6 +27,7 @@
 atm_db_VZA = np.array([0, 5, 10, 15, 20, 25, 30, 40]) # view zenith angle, in [deg]
 atm_db_RAA = np.array([0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180]) # relative azimuth angle, in [deg]
 
+
 def build_atm_lut(flight_dict):
     """ Make an atmospheric lookup table.
 
@@ -154,6 +159,7 @@ def build_atm_lut(flight_dict):
 
     logger.info('Write the raw ALT to %s.' %flight_dict['raw_atm_lut_file'])
 
+
 def resample_atm_lut(resampled_atm_lut_file, raw_atm_lut_file, rdn_header_file):
     """ Resample atmosphere lookup table radiance to sensor wavelengths.
 
@@ -218,6 +224,7 @@ def resample_atm_lut(resampled_atm_lut_file, raw_atm_lut_file, rdn_header_file):
 
     logger.info('Write the resampled ALT to %s.' %resampled_atm_lut_file)
 
+
 def write_binary_metadata(metadata_file, metadata):
     """ Write the metadata of a binary file.
 
@@ -246,6 +253,7 @@ def write_binary_metadata(metadata_file, metadata):
         fid.write('%s = %s\n' %(key, value))
     fid.close()
 
+
 def read_binary_metadata(metadata_file):
     """ Read the metadata of a binary file.
 
@@ -286,6 +294,7 @@ def read_binary_metadata(metadata_file):
 
     return metadata
 
+
 def get_interp_range(xs, x):
     """ Get the interpolation range. """
 
@@ -296,6 +305,7 @@ def get_interp_range(xs, x):
 
     return {x_index0: x_delta0, x_index1: x_delta1}
 
+
 def combos(indices):
     """ Return all combinations of indices in a list of index sublists.
 
diff --git a/hypro/Boresight.py b/hypro/Boresight.py
index 5546e2d..3d24b8a 100644
--- a/hypro/Boresight.py
+++ b/hypro/Boresight.py
@@ -9,9 +9,14 @@
 
 """ Functions to do boresight calibration. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
+
 def boresight_calibration(boresight_file, gcp_file, imugps_file, sensor_model_file, dem_image_file, boresight_options):
     """ Do boresight calibration.
 
@@ -145,6 +150,7 @@ def boresight_calibration(boresight_file, gcp_file, imugps_file, sensor_model_fi
 
     logger.info('Write boresight data to %s.' %boresight_file)
 
+
 def cost_fun(boresight_offsets, flight_xyz, flight_imu, flight_sensor_model, dem_image, dem_ulxy, dem_pixel_size, gcp_xyz, boresight_options):
     """ Cost function for boresight calibration.
 
@@ -178,6 +184,7 @@ def cost_fun(boresight_offsets, flight_xyz, flight_imu, flight_sensor_model, dem
 
     return cost
 
+
 def estimate_gcp_xyz(boresight_offsets, flight_xyz, flight_imu, flight_sensor_model, dem_image, dem_ulxy, dem_pixel_size, boresight_options):
     """ Cestimate GCP map coordinates.
 
diff --git a/hypro/Classification.py b/hypro/Classification.py
index 7935c80..8e5684b 100644
--- a/hypro/Classification.py
+++ b/hypro/Classification.py
@@ -9,11 +9,16 @@
 
 """ Functions to do image classifications. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
 solar_flux_file = os.path.join(os.path.dirname(os.path.realpath(__file__)),'data','solar_flux.dat')
 
+
 def pre_classification(pre_class_image_file, rdn_image_file, sun_zenith, distance, background_mask_file=None):
     """ Pre-classify the image.
 
diff --git a/hypro/CreateSCA.py b/hypro/CreateSCA.py
index 5998da3..803e088 100644
--- a/hypro/CreateSCA.py
+++ b/hypro/CreateSCA.py
@@ -7,9 +7,10 @@
 # Dept. of Forest and Wildlife Ecology
 # University of Wisconsin - Madison
 
-from ENVI import read_envi_header, write_envi_header
 import numpy as np
 
+from ENVI import read_envi_header, write_envi_header
+
 if __name__ == "__main__":
 
     raw_sca_file = '/media/nanfeng/My Passport/Hyspex/Output/CEDAR-CREEK-EW_20180724_01/merge/CEDAR-CREEK-EW_20180724_01_SCA'
diff --git a/hypro/DEM.py b/hypro/DEM.py
index 0b658f2..f23db93 100644
--- a/hypro/DEM.py
+++ b/hypro/DEM.py
@@ -9,10 +9,15 @@
 
 """ Functions to process DEM data. """
 
+import os
+import logging
+
+import numpy as np
 from osgeo import gdal
-import logging, os, numpy as np
+
 logger = logging.getLogger(__name__)
 
+
 def get_avg_elev(dem_image_file):
     """ Get the average elevation of a DEM image.
 
@@ -39,6 +44,7 @@ def get_avg_elev(dem_image_file):
 
     return avg_elev
 
+
 def prepare_dem(dem_image_file, dem, imugps_file, fov, map_crs, pixel_size):
     """ Prepare DEM data.
 
diff --git a/hypro/ENVI.py b/hypro/ENVI.py
index 05008ad..cb49737 100644
--- a/hypro/ENVI.py
+++ b/hypro/ENVI.py
@@ -113,6 +113,7 @@
                'z plot range',
                'z plot titles']
 
+
 def read_envi_header(file):
     """ Read ENVI header.
 
@@ -164,6 +165,7 @@ def read_envi_header(file):
 
     return header
 
+
 def check_envi_required_fields(header):
     """ Check ENVI required fields.
 
@@ -183,6 +185,7 @@ def check_envi_required_fields(header):
         if header[field] is None:
             raise ValueError('No value for %s!' %field)
 
+
 def empty_envi_header():
     """ Generate an empty ENVI header.
 
@@ -198,6 +201,7 @@ def empty_envi_header():
 
     return header
 
+
 def write_envi_header(file, header):
     """ Write ENVI header.
 
diff --git a/hypro/Figure.py b/hypro/Figure.py
index ed5a604..e9f27c2 100644
--- a/hypro/Figure.py
+++ b/hypro/Figure.py
@@ -9,13 +9,18 @@
 
 """ Functions to make figures. """
 
-import logging, os, matplotlib.pyplot as plt, numpy as np
+import os
+import logging
+
+import numpy as np
 from osgeo import gdal
+import matplotlib.pyplot as plt
 
 mpl_logger = logging.getLogger('matplotlib')
 mpl_logger.setLevel(logging.WARNING)
 logger = logging.getLogger(__name__)
 
+
 def plot_angle_geometry(angle_geometry_figure_file, sca_image_file):
     """ Plot the sun-target-view geometry in a polar coordinate system.
 
@@ -60,6 +65,7 @@ def plot_angle_geometry(angle_geometry_figure_file, sca_image_file):
 
     logger.info('Save the angle geometry figure to %s.' %angle_geometry_figure_file)
 
+
 def plot_image_area(image_area_figure_file, dem_image_file, igm_image_file, imugps_file):
     """ Plot image area (DEM is used as the background).
 
@@ -124,6 +130,7 @@ def plot_image_area(image_area_figure_file, dem_image_file, igm_image_file, imug
 
     logger.info('Save the image-area figure to %s.' %image_area_figure_file)
 
+
 def linear_percent_stretch(raw_image):
     """ Do linear percent stretch.
 
@@ -153,6 +160,7 @@ def linear_percent_stretch(raw_image):
 
     return stretched_image
 
+
 def make_quicklook(quicklook_figure_file, rdn_image_file, glt_image_file):
     """ Make a RGB quicklook image.
 
@@ -235,6 +243,7 @@ def make_quicklook(quicklook_figure_file, rdn_image_file, glt_image_file):
 
     logger.info('Save the quicklook figure to %s.' %quicklook_figure_file)
 
+
 def plot_avg_rdn(avg_rdn_figure_file, avg_rdn_file):
     """ Plot average radiance to a figure.
 
@@ -273,6 +282,7 @@ def plot_avg_rdn(avg_rdn_figure_file, avg_rdn_file):
 
     logger.info('Save the average radiance spectra figure to %s.' %avg_rdn_figure_file)
 
+
 def plot_wvc_model(wvc_model_figure_file, wvc_model_file):
     """ Plot the WVC model to a figure.
 
@@ -312,6 +322,7 @@ def plot_wvc_model(wvc_model_figure_file, wvc_model_file):
 
     logger.info('Save the WVC model figure to %s.' %wvc_model_file)
 
+
 def plot_smile_effect(smile_effect_at_atm_features_figure_file, smile_effect_at_atm_features_file):
     """ Plot smile effects at different atmosphere absorption features.
 
@@ -412,6 +423,7 @@ def plot_smile_effect(smile_effect_at_atm_features_figure_file, smile_effect_at_
 
     logger.info('Save smile effect at atmosphere absorption features figure to %s.' %smile_effect_at_atm_features_figure_file)
 
+
 def plot_wvc_histogram(wvc_histogram_figure_file, water_vapor_column_image_file):
     """ Plot water vapor column histogram.
 
diff --git a/hypro/GeoRectification.py b/hypro/GeoRectification.py
index 48bdcbd..e7717a0 100644
--- a/hypro/GeoRectification.py
+++ b/hypro/GeoRectification.py
@@ -9,9 +9,14 @@
 
 """ Functions to do geo-rectification. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
+
 def orthorectify_sca(ortho_sca_image_file, sca_image_file, glt_image_file):
     """ Do orthorectifications on SCA.
 
@@ -88,6 +93,7 @@ def orthorectify_sca(ortho_sca_image_file, sca_image_file, glt_image_file):
 
     logger.info('Write the geo-rectified SCA image to %s.' %ortho_sca_image_file)
 
+
 def orthorectify_dem(ortho_dem_image_file, igm_image_file, glt_image_file):
     """ Do orthorectifications on DEM.
 
@@ -160,6 +166,7 @@ def orthorectify_dem(ortho_dem_image_file, igm_image_file, glt_image_file):
 
     logger.info('Write the geo-rectified DEM image to %s.' %ortho_dem_image_file)
 
+
 def orthorectify_rdn(ortho_rdn_image_file, rdn_image_file, glt_image_file):
     """ Do orthorectifications on radiance.
 
diff --git a/hypro/GeoReferencing.py b/hypro/GeoReferencing.py
index 3a3d40f..957a4dd 100644
--- a/hypro/GeoReferencing.py
+++ b/hypro/GeoReferencing.py
@@ -9,13 +9,20 @@
 
 """ Functions to do geo-referencing. """
 
+import os
+import logging
+import warnings
+
+import numpy as np
 from osgeo import gdal
-import logging, os, numpy as np
-logger = logging.getLogger(__name__)
 from numba import guvectorize, jit
-import warnings
+
+
+logger = logging.getLogger(__name__)
+
 warnings.filterwarnings("ignore")
 
+
 def calculate_igm(igm_image_file, imugps_file, sensor_model_file, dem_image_file, boresight_options):
     """ Create an input geometry (IGM) image.
 
@@ -137,6 +144,7 @@ def calculate_igm(igm_image_file, imugps_file, sensor_model_file, dem_image_file
 
     logger.info('Write the IGM to %s.' %igm_image_file)
 
+
 def calculate_sca(sca_image_file, imugps_file, igm_image_file, sun_angles):
     """ Create a scan angle (SCA) image.
 
@@ -223,6 +231,7 @@ def calculate_sca(sca_image_file, imugps_file, igm_image_file, sun_angles):
 
     logger.info('Write the SCA to %s.' %sca_image_file)
 
+
 def build_glt(glt_image_file, igm_image_file, pixel_size, map_crs):
     """ Create a geographic lookup table (GLT) image.
 
@@ -417,6 +426,7 @@ def build_glt(glt_image_file, igm_image_file, pixel_size, map_crs):
 
     logger.info('Write the GLT to %s.' %glt_image_file)
 
+
 def get_scan_vectors(imu, sensor_model):
     """ Get scan vectors.
 
@@ -507,6 +517,7 @@ def get_scan_vectors(imu, sensor_model):
 
     return L0
 
+
 def get_xyz0_xyz1(xyz, L0, h_min, h_max):
     """ Get the starting and ending locations of ray tracing.
 
@@ -548,6 +559,7 @@ def get_xyz0_xyz1(xyz, L0, h_min, h_max):
 
     return xyz0, xyz1
 
+
 @guvectorize(['void(f8[:,:,:], f8[:,:,:], f8[:,:,:], f8[:,:], f8[:], f8[:,:,:])'],
              '(b,n,m), (b,n,m), (b,n,m), (u,v), (c) -> (b,m,n)', cache=True)
 def ray_tracer_ufunc(xyz0, xyz1, L0, dem, dem_gt, output):
@@ -596,6 +608,7 @@ def ray_tracer_ufunc(xyz0, xyz1, L0, dem, dem_gt, output):
         for j in range(xyz0.shape[2]): # Iterate over scanlines
             output[:,j,i] = ray_tracing(xyz0[:,i,j], xyz1[:,i,j], L0[:,i,j], dem, dem_origin, resolution)
 
+
 @jit
 def ray_tracing(XYZ0, XYZ1, V, DEM, DEM_X0Y0, DEM_Resolution):
     """ Implement ray-tracing to get the pixel's geo-location and elevation.
diff --git a/hypro/Geography.py b/hypro/Geography.py
index fe83eec..acbe89d 100644
--- a/hypro/Geography.py
+++ b/hypro/Geography.py
@@ -9,8 +9,11 @@
 
 """ Functions to process map coordinate systems. """
 
+import os
+
+import numpy as np
 from osgeo import gdal, osr
-import os, numpy as np
+
 
 def get_utm_zone(lon):
     """ Calculate UTM zone.
@@ -30,6 +33,7 @@ def get_utm_zone(lon):
 
     return zone
 
+
 def is_northern(lat):
     """ Determine if it is northern hemisphere.
 
@@ -49,6 +53,7 @@ def is_northern(lat):
     else:
         return 1
 
+
 def define_utm_crs(lon, lat):
     """ Define a UTM map coordinate system.
 
@@ -72,6 +77,7 @@ def define_utm_crs(lon, lat):
 
     return crs
 
+
 def define_wgs84_crs():
     """ Define a WGS84 map coordinate system.
 
@@ -86,6 +92,7 @@ def define_wgs84_crs():
 
     return crs
 
+
 def get_raster_crs(file):
     """ Get the map coordinate system of a raster image.
 
@@ -109,6 +116,7 @@ def get_raster_crs(file):
 
     return crs
 
+
 def get_grid_convergence(lon, lat, map_crs):
     """ Get grid convergence angles.
 
@@ -149,6 +157,7 @@ def get_grid_convergence(lon, lat, map_crs):
 
     return grid_convergence
 
+
 def get_map_crs(dem, longitude, latitude):
     """ Get map coordinate system.
 
@@ -178,6 +187,7 @@ def get_map_crs(dem, longitude, latitude):
 
     return map_crs
 
+
 def get_sun_angles(longitude, latitude, utc_time):
     """ Calculate the Sun's position.
 
diff --git a/hypro/HyspexPro.py b/hypro/HyspexPro.py
index 3c43664..552036a 100644
--- a/hypro/HyspexPro.py
+++ b/hypro/HyspexPro.py
@@ -151,6 +151,7 @@
 from VIS              import estimate_vis
 from AtmCorr          import atm_corr_image
 
+
 def get_flight_indices(config):
     """ Get Hyspex flight indices.
 
@@ -177,6 +178,7 @@ def get_flight_indices(config):
 
     return flight_indices
 
+
 def create_flight_log(output_dir, log_file_basename):
     """ Create a Hyspex flight processing log.
 
@@ -203,6 +205,7 @@ def create_flight_log(output_dir, log_file_basename):
 
     return flight_log
 
+
 def initialize_flight_dict(config, flight_index):
     """ Initialize a Hyspex flight dictionary.
 
@@ -292,6 +295,7 @@ def initialize_flight_dict(config, flight_index):
 
     return flight_dict
 
+
 def search_file(in_dir, keyword):
     """ Search a specific file with the keyword.
 
@@ -317,6 +321,7 @@ def search_file(in_dir, keyword):
     else:
         return file[0]
 
+
 def get_center_lon_lat(raw_imugps_file):
     """ Get Hyspex image center longitude and latitude.
 
@@ -339,6 +344,7 @@ def get_center_lon_lat(raw_imugps_file):
 
     return [lon, lat]
 
+
 def get_acquisition_time(dn_header_file, raw_imugps_file):
     """ Get Hyspex image acquistion time.
 
@@ -374,6 +380,7 @@ def get_acquisition_time(dn_header_file, raw_imugps_file):
 
     return when
 
+
 def get_sun_earth_distance(when):
     """ Get sun-earth distance of a day.
 
@@ -396,6 +403,7 @@ def get_sun_earth_distance(when):
 
     return d
 
+
 def HyspexPro(config_file):
     # Load configurations.
     config = json.load(open(config_file, 'r'))
diff --git a/hypro/IMUGPS.py b/hypro/IMUGPS.py
index c553fa5..4ddeca2 100644
--- a/hypro/IMUGPS.py
+++ b/hypro/IMUGPS.py
@@ -13,6 +13,7 @@
 import logging, os, numpy as np
 logger = logging.getLogger(__name__)
 
+
 def prepare_imugps_Hyspex(processed_imugps_file, raw_imugps_file, boresight_offsets, map_crs, boresight_options):
     """ Prepare Hyspex IMU and GPS data.
 
diff --git a/hypro/ImageMerging.py b/hypro/ImageMerging.py
index 4f7474e..3929421 100644
--- a/hypro/ImageMerging.py
+++ b/hypro/ImageMerging.py
@@ -9,8 +9,14 @@
 
 """ Functions to merge images from different sensors. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
+
+
 def merge_dem_sca(background_mask_file, merged_dem_file, merged_sca_file, sensors):
     """ Merge DEM and SCA images.
 
@@ -229,6 +235,7 @@ def merge_dem_sca(background_mask_file, merged_dem_file, merged_sca_file, sensor
     del raw_header, header
     logger.info('Write the merged SCA image to %s.' %merged_sca_file)
 
+
 def merge_rdn(merged_image_file, mask_file, sensors):
     """ Merge radiance images.
 
@@ -337,6 +344,7 @@ def merge_rdn(merged_image_file, mask_file, sensors):
 
     logger.info('Write the merged refletance image to %s.' %merged_image_file)
 
+
 def resample_ortho_sca(raw_image, raw_ulx, raw_uly, raw_pixel_size, x, y):
     """ Resample geosca image to new map grids.
 
@@ -377,6 +385,7 @@ def resample_ortho_sca(raw_image, raw_ulx, raw_uly, raw_pixel_size, x, y):
 
     return resampled_image
 
+
 def resample_ortho_dem(raw_image, raw_ulx, raw_uly, raw_pixel_size, x, y):
     """ Resample dem image to new map grids.
 
@@ -417,6 +426,7 @@ def resample_ortho_dem(raw_image, raw_ulx, raw_uly, raw_pixel_size, x, y):
 
     return resampled_image
 
+
 def resample_ortho_rdn(raw_image, raw_ulx, raw_uly, raw_pixel_size, x, y):
     """ Resample radiance image to new map grids.
 
diff --git a/hypro/Radiometry.py b/hypro/Radiometry.py
index 2cd527f..bc3ff2e 100644
--- a/hypro/Radiometry.py
+++ b/hypro/Radiometry.py
@@ -9,9 +9,14 @@
 
 """ Functions to do radiometric calibrations. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
+
 def make_radio_cali_file_Hyspex(radio_cali_file, dn_image_file, setting_file):
     """ Make a Hyspex radiometric calibration file.
 
@@ -222,6 +227,7 @@ def from_int8array_to_string(int8_array):
 
     logger.info('Write the radiometric calibration coefficients to %s.' %radio_cali_file)
 
+
 def dn2rdn_Hyspex(rdn_image_file, dn_image_file, radio_cali_file, acquisition_time):
     """ Do Hyspex radiometric calibration.
 
@@ -325,6 +331,7 @@ def dn2rdn_Hyspex(rdn_image_file, dn_image_file, radio_cali_file, acquisition_ti
 
     logger.info('Write the radiance image to %s.' %rdn_image_file)
 
+
 def resample_rdn(resampled_rdn_image_file, raw_rdn_image_file, smile_effect_file):
     """ Resample radiance spectra.
 
@@ -402,6 +409,7 @@ def resample_rdn(resampled_rdn_image_file, raw_rdn_image_file, smile_effect_file
 
     logger.info('Write the spectrally resampled radiance image to %s.' %resampled_rdn_image_file)
 
+
 def get_hyspex_setting(setting_file):
     """ Read Hyspex setting data.
 
diff --git a/hypro/SensorModel.py b/hypro/SensorModel.py
index 2e7793e..eccbbcb 100644
--- a/hypro/SensorModel.py
+++ b/hypro/SensorModel.py
@@ -9,9 +9,14 @@
 
 """ Functions to create a sensor model. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
+
 def make_sensor_model(sensor_model_file, fov, ifov, samples, if_rotated):
     """ Generate a sensor model.
 
@@ -52,6 +57,7 @@ def make_sensor_model(sensor_model_file, fov, ifov, samples, if_rotated):
 
     logger.info('Write the sensor model to %s.' %sensor_model_file)
 
+
 def determine_if_rotated(imu_gps_file):
     """ Determine if the sensor is 180 degree rotated.
 
diff --git a/hypro/SmileEffect.py b/hypro/SmileEffect.py
index d90f383..57ad7b6 100644
--- a/hypro/SmileEffect.py
+++ b/hypro/SmileEffect.py
@@ -9,7 +9,11 @@
 
 """ Functions to detect smile effects. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
 # Define atmosphere absorption features.
@@ -31,6 +35,7 @@
                        2420: [2400, 2435]
                        }
 
+
 def detect_smile_effect(sensor_dict, atm_lut_file):
     """ Detect smile effect.
 
@@ -232,6 +237,7 @@ def detect_smile_effect(sensor_dict, atm_lut_file):
 
     logger.info('Write smile effect to %s.' %sensor_dict['smile_effect_file'])
 
+
 def interp_atm_lut(atm_lut_file, WVC, VIS, VZA, RAA):
     """ Interpolate atmosphere look-up-table to different water vapor columns (WVC),
         visibilities (VIS), view zenith angles (VZA) and relative azimuth angles (RAA).
@@ -296,6 +302,7 @@ def interp_atm_lut(atm_lut_file, WVC, VIS, VZA, RAA):
 
     return atm_lut_WAVE, interp_rdn
 
+
 def average_rdn(avg_rdn_file, rdn_image_file, sca_image_file, pre_class_image_file):
     """ Average radiance along each column.
 
@@ -407,6 +414,7 @@ def average_rdn(avg_rdn_file, rdn_image_file, sca_image_file, pre_class_image_fi
 
     logger.info('Write the averaged radiance data to %s.' %avg_rdn_file)
 
+
 def interpolate_values(A, map):
     """ Replace array elements with interpolated values. Input array is modified in-place.
 
@@ -421,6 +429,7 @@ def interpolate_values(A, map):
     def indices(x): return x.nonzero()[0]
     A[map] = np.interp(indices(map), indices(~map), A[~map])
 
+
 def cost_fun(shifts, sensor_wave, sensor_fwhm, sensor_rdn, lut_wave, lut_rdn):
     """ Cost function.
 
diff --git a/hypro/Spectra.py b/hypro/Spectra.py
index c2c1182..9ecbd3c 100644
--- a/hypro/Spectra.py
+++ b/hypro/Spectra.py
@@ -15,10 +15,13 @@
         https://github.com/EnSpec/HyTools-sandbox/blob/master/hytools/preprocess/resampling.py
 """
 
-import numpy as np
 import warnings
+
+import numpy as np
+
 warnings.filterwarnings("ignore", category=FutureWarning)
 
+
 def estimate_fwhms_from_waves(waves):
     """ Estimate fwhm from wavelengths.
 
@@ -39,6 +42,7 @@ def estimate_fwhms_from_waves(waves):
 
     return fwhms
 
+
 def gaussian(x, mu, fwhm):
     """ Return a gaussian distribution.
 
@@ -60,6 +64,7 @@ def gaussian(x, mu, fwhm):
 
     return np.exp(-1*((x-mu)**2/(2*sigma**2)))/(sigma*np.sqrt(2*np.pi))
 
+
 def resample_spectra(spectra, src_waves, dst_waves, dst_fwhms, src_fwhms=None):
     """ Return a set of coeffiencients for spectrum resampling.
 
@@ -123,6 +128,7 @@ def resample_spectra(spectra, src_waves, dst_waves, dst_fwhms, src_fwhms=None):
 
     return resampled_spectra
 
+
 def get_closest_wave(waves, center_wave):
     """ Get the band index whose wavelength is closest to `center_wav`.
 
@@ -143,6 +149,7 @@ def get_closest_wave(waves, center_wave):
 
     return waves[band_index], band_index
 
+
 def continuum_removal(spectra, waves):
     """Continuum remove spectra.
 
@@ -165,6 +172,7 @@ def continuum_removal(spectra, waves):
 
     return cont_rmd_spectra
 
+
 def resample_solar_flux(solar_flux_file, sensor_waves, sensor_fwhms):
     """ Resample solar flux to sensor wavelengths.
 
diff --git a/hypro/VIS.py b/hypro/VIS.py
index bad1142..5dd119a 100644
--- a/hypro/VIS.py
+++ b/hypro/VIS.py
@@ -9,7 +9,10 @@
 
 """ Functions to estimate visibility. """
 
-import logging, os, numpy as np
+import os
+import logging
+import numpy as np
+
 logger = logging.getLogger(__name__)
 
 # Define typical water vapor column values of the atmosphere database. Do not make any change to them.
@@ -20,6 +23,7 @@
                   'midlatitude_summer': 29.2,
                   'tropical': 41.1}
 
+
 def estimate_vis(vis_file, ddv_file, atm_lut_file, rdn_file, sca_file, background_mask_file):
     """ Estimate visibility.
 
@@ -231,6 +235,7 @@ def estimate_vis(vis_file, ddv_file, atm_lut_file, rdn_file, sca_file, backgroun
     # Clear data
     del ndvi, red_refl, nir_refl, rdn_header
 
+
 def interp_atm_lut(atm_lut_RHO, atm_lut_WVC, atm_lut_VZA, atm_lut_RAA, atm_lut, rho, wvc, vza, raa):
     """ Interpolate the atmospheric lookup table for visibility estimation.
 
diff --git a/hypro/WVC.py b/hypro/WVC.py
index cceca36..211cfb0 100644
--- a/hypro/WVC.py
+++ b/hypro/WVC.py
@@ -9,10 +9,15 @@
 
 """ Functions to estimate water vapor column. """
 
-import logging, os, numpy as np
+import os
+import logging
+
+import numpy as np
+
 logger = logging.getLogger(__name__)
 solar_flux_file = os.path.join(os.path.dirname(os.path.realpath(__file__)),'data','solar_flux.dat')
 
+
 def build_wvc_model(wvc_model_file, atm_lut_file, rdn_header_file, vis=40):
     """ Build water vapor models.
 
@@ -122,6 +127,7 @@ def build_wvc_model(wvc_model_file, atm_lut_file, rdn_header_file, vis=40):
         json.dump(wvc_model, fid, indent=4)
     logger.info('Write WVC models to %s.' %wvc_model_file)
 
+
 def estimate_wvc(wvc_file, rdn_file, sensors, sun_zenith, distance, background_mask_file):
     """ Estimate water vapor column.