"""
This module contains corrections for micropulse lidars
"""
import warnings
import numpy as np
import xarray as xr
[docs]def correct_mpl(
ds,
co_pol_var_name='signal_return_co_pol',
cross_pol_var_name='signal_return_cross_pol',
co_pol_afterpuls_var_name='afterpulse_correction_co_pol',
cross_pol_afterpulse_var_name='afterpulse_correction_cross_pol',
overlap_corr_var_name='overlap_correction',
overlap_corr_heights_var_name='overlap_correction_heights',
range_bins_var_name='range_bins',
height_var_name='height',
ratio_var_name='cross_co_ratio',
):
"""
This procedure corrects MPL data:
1.) Throw out data before laser firing (heights < 0).
2.) Remove background signal.
3.) Afterpulse Correction - Subtraction of (afterpulse-darkcount).
NOTE: Currently the Darkcount in VAPS is being calculated as
the afterpulse at ~30km. But that might not be absolutely
correct and we will likely start providing darkcount profiles
ourselves along with other corrections.
4.) Range Correction.
5.) Overlap Correction (Multiply).
If the height variable changes between netCDF files, Xarray will turn the height
dimention variables from a 1D to a 2D array. This will cause issues with processing
and other data manipulation. To fix this the 2D height will be converted to a 1D
array by using the median value for each height value.
Note: Deadtime and darkcount corrections are not being applied yet.
Parameters
----------
ds : xarray.Dataset
The Xarray Dataset containing data
co_pol_var_name : str
The Co-polar variable name used in Dataset
cross_pol_var_name : str
The Cross-polar variable name used in Dataset
co_pol_afterpuls_var_name : str
The Co-polar after pulse variable name used in Dataset
cross_pol_afterpulse_var_name : str
The Cross-polar afterpulse variable name used in Dataset
overlap_corr_var_name : str
The overlap correction variable name used in Dataset
overlap_corr_heights_var_name : str
The overlap correction height variable name used in Dataset
range_bins_var_name : str
The range bins variable name used in Dataset
height_var_name : str
The height variable name used in Dataset
ratio_var_name : str
The variable name to use for newly created variable of co/cross ratio.
Set to None if do not want this new variables created in Dataset.
Returns
-------
ds : xarray.Dataset
Xarray dataset containing the corrected values. The original Xarray Dataset
passed in is modified.
"""
data_dims = ds[co_pol_var_name].dims
# Overlap Correction Variable
op = ds[overlap_corr_var_name].values
if len(op.shape) > 1:
op = op[0, :]
op_height = ds[overlap_corr_heights_var_name].values
if len(op_height.shape) > 1:
op_height = op_height[0, :]
# Check if height has dimentionality of time and height. If so reduce
# height to only dimentionality of height in the dataset before removing
# values less than 0.
if len(ds[height_var_name].shape) > 1:
reduce_dim_name = {'time'} & set(ds[height_var_name].dims)
ds[height_var_name] = ds[height_var_name].reduce(
func=np.median, dim=reduce_dim_name, keep_attrs=True
)
# 1 - Remove negative height data
ds = ds.where(ds[height_var_name] > 0.0, drop=True)
height = ds[height_var_name].values
# Get indices for calculating background
if len(ds.height.shape) > 1:
ind = [ds.height.shape[1] - 50, ds.height.shape[1] - 2]
else:
ind = [ds.height.shape[0] - 50, ds.height.shape[0] - 2]
# Subset last gates into new dataset
dummy = ds.isel(range_bins=xr.DataArray(np.arange(ind[0], ind[1])))
# Turn off warnings
warnings.filterwarnings('ignore')
# Run through co and cross pol data for corrections
co_bg = dummy[co_pol_var_name]
co_bg = co_bg.where(co_bg > -9998.0)
co_bg = co_bg.mean(dim='dim_0').values
x_bg = dummy[cross_pol_var_name]
x_bg = x_bg.where(x_bg > -9998.0)
x_bg = x_bg.mean(dim='dim_0').values
# Seems to be the fastest way of removing background signal at the moment
co_data = ds[co_pol_var_name].where(ds[co_pol_var_name] > 0).values
x_data = ds[cross_pol_var_name].where(ds[cross_pol_var_name] > 0).values
for i in range(len(ds['time'].values)):
co_data[i, :] = co_data[i, :] - co_bg[i]
x_data[i, :] = x_data[i, :] - x_bg[i]
# After Pulse Correction Variable
co_ap = ds[co_pol_afterpuls_var_name].values
# Fix dimentionality if backwards
co_ap_dims = ds[co_pol_afterpuls_var_name].dims
if len(co_ap_dims) > 1 and co_ap_dims[::-1] == data_dims:
co_ap = np.transpose(co_ap)
x_ap = ds[cross_pol_afterpulse_var_name].values
# Fix dimentionality if backwards
x_ap_dims = ds[cross_pol_afterpulse_var_name].dims
if len(x_ap_dims) > 1 and x_ap_dims[::-1] == data_dims:
x_ap = np.transpose(x_ap)
# Afterpulse Correction
co_data = co_data - co_ap
x_data = x_data - x_ap
# R-Squared Correction
co_data = co_data * height**2
x_data = x_data * height**2
# Overlap Correction
for j in range(ds[range_bins_var_name].size):
if len(height.shape) > 1:
idx = (np.abs(op_height - height[0, j])).argmin()
else:
# Overlap Correction
idx = (np.abs(op_height - height[j])).argmin()
co_data[:, j] = co_data[:, j] * op[idx]
x_data[:, j] = x_data[:, j] * op[idx]
# Create the co/cross ratio variable
if ratio_var_name is not None:
ratio = (x_data / (x_data + co_data)) * 100.0
ds[ratio_var_name] = ds[co_pol_var_name].copy(data=ratio)
ds[ratio_var_name].attrs['long_name'] = 'Cross-pol / Co-pol ratio * 100'
ds[ratio_var_name].attrs['units'] = 'LDR'
try:
del ds[ratio_var_name].attrs['ancillary_variables']
del ds[ratio_var_name].attrs['description']
except KeyError:
pass
# Convert data to decibels
co_data = 10.0 * np.log10(co_data)
x_data = 10.0 * np.log10(x_data)
# Write data to Xarray dataset
ds[co_pol_var_name].values = co_data
ds[cross_pol_var_name].values = x_data
# Update units
ds[co_pol_var_name].attrs['units'] = f"10 * log10({ds[co_pol_var_name].attrs['units']})"
ds[cross_pol_var_name].attrs['units'] = f"10 * log10({ds[cross_pol_var_name].attrs['units']})"
return ds