python -- 替换netcdf文件中的时间

• 最近，在处理nc文件时，在时间上存在部分缺失的数据，为了避免影响后续操作，这里通过复制前一时刻的nc数据进行替代，但是虽然缺失时刻的数据得到了填充，但是填充的数据的时间属性本质上仍然是前一时刻的，为了保证时间的一致性，这里通过一个更新时间的脚本，进行替换。
• 脚本如下，在shell脚本中，需要传递两个参数给该python脚本，一个为需要替换时间的nc文件的完整路径，第二个为替换的时间。

import netCDF4 as nc
import datetime

def update_time_in_ncfile(input_file, new_time):
    try:
        # Open the NetCDF file in read-write mode
        with nc.Dataset(input_file, 'a') as dataset:
            # Assuming you have a 'time' variable in the NetCDF file
            if 'time' in dataset.variables:
                time_var = dataset.variables['time']
                # Convert the new time string to a datetime object
                new_time_obj = datetime.datetime.strptime(new_time, '%Y%m%d %H%M')
                # Convert the datetime object to the units used in the 'time' variable
                new_time_units = f"seconds since {new_time_obj.strftime('%Y-%m-%d %H:%M:%S')}"
                # Update the time variable's units and values
                time_var.units = new_time_units
                time_var[:] = [0.0]  # You may need to adjust this value depending on the units

            # Save the changes
            dataset.sync()
            print(f"Time in {input_file} updated to {new_time}")

    except Exception as e:
        print(f"Error updating time in {input_file}: {str(e)}")

if __name__ == "__main__":
    input_file = "/Users/test_code/NC_HS_H09_20230620_0110_FLDK_R100.nc"  # Replace with the actual input file path
    new_time = "20230621 1234"  # Replace with the desired new time

    update_time_in_ncfile(input_file, new_time)

这里利用shell脚本进行传递，以下是shell脚本的内容，仅提供一个封装好的函数：

process_folder() {
  local folder_path=$1
  if [[ -d $folder_path ]]; then
    echo "Processing files in $folder_path..."
    output_file="${temp_nc_path}/NC_HS_H09_${date_str}_${time_str}_FLDK_R100.nc"

    if [ ! -f "$output_file" ]; then
      /home/software/miniconda/envs/tf-g/bin/python "$convert_script" \
        --root_path "$1" \
        --temp_path "$temp_path" \
        --temp_nc_path "$temp_nc_path" \
        --bin_path "$bin_path"\
	 > "$python_output" 2>&1
      if [ $? -ne 0 ]; then
        echo "Error processing files in $folder_path. Check $python_output for details."
      fi
    else
      echo "Output file $output_file already exists"
   
    fi
  else
    echo "Folder $folder_path does not exist. Copying from previous time step..."
    output_file="${temp_nc_path}/NC_HS_H09_${date_str}_${time_str}_FLDK_R100.nc"
    prev_time_str=$(date -d "$time_str - 10 minutes" "+%H%M")
    prev_output_file="${temp_nc_path}/NC_HS_H09_${date_str}_${prev_time_str}_FLDK_R100.nc"
    echo "prev_time_str:$prev_time_str prev_output_file:$prev_output_file"
    cp "$prev_output_file" "$output_file"
    /home/software/miniconda/envs/tf-g/bin/python "/home/gaby/test_run/code/time_up.py" "$output_file" "${date_str} ${time_str}"
  fi
}

以上，通过shell脚本与python脚本的结合，初步实现了缺失时刻的nc数据的填充。对于海表面温度（SST）、海面风速等海洋要素特征来说，短时间内变化不那么剧烈，可以采用上述方法；当然，这里展示的只是通过复制前一时刻的数据，也可以通过插值的方法，这就需要额外编写相关的python脚本，然后加到对应的if / else 判断下。