satpy.readers.ahi_hsd module

Advanced Himawari Imager (AHI) standard format data reader.

References

Time Information

AHI observations use the idea of a “scheduled” time and an “observation time. The “scheduled” time is when the instrument was told to record the data, usually at a specific and consistent interval. The “observation” time is when the data was actually observed. Scheduled time can be accessed from the scheduled_time metadata key and observation time from the start_time key.

class satpy.readers.ahi_hsd.AHIHSDFileHandler(filename, filename_info, filetype_info, mask_space=True, calib_mode='update', user_calibration=None)[source]

Bases: satpy.readers.file_handlers.BaseFileHandler

AHI standard format reader.

The AHI sensor produces data for some pixels outside the Earth disk (i,e: atmospheric limb or deep space pixels). By default, these pixels are masked out as they contain data of limited or no value, but some applications do require these pixels. It is therefore possible to override the default behaviour and perform no masking of non-Earth pixels.

In order to change the default behaviour, use the ‘mask_space’ variable as part of reader_kwargs upon Scene creation:

import satpy
import glob

filenames = glob.glob('*FLDK*.dat')
scene = satpy.Scene(filenames,
                    reader='ahi_hsd',
                    reader_kwargs={'mask_space': False})
scene.load([0.6])

The AHI HSD data files contain multiple VIS channel calibration coefficients. By default, the updated coefficients in header block 6 are used. If the user prefers the default calibration coefficients from block 5 then they can pass calib_mode=’nominal’ when creating a scene:

import satpy
import glob

filenames = glob.glob('*FLDK*.dat')
scene = satpy.Scene(filenames,
                    reader='ahi_hsd',
                    reader_kwargs={'calib_mode': 'update'})
scene.load([0.6])

Alternative AHI calibrations are also available, such as GSICS coefficients. As such, you can supply custom per-channel correction by setting calib_mode=’custom’ and passing correction factors via:

user_calibration={'chan': ['slope': slope, 'offset': offset]}

Where slo and off are per-channel slope and offset coefficients defined by:

rad_leo = (rad_geo - off) / slo

If you do not have coefficients for a particular band, then by default the slope will be set to 1 .and the offset to 0.:

import satpy
import glob

# Load bands 7, 14 and 15, but we only have coefs for 7+14
calib_dict = {'B07': {'slope': 0.99, 'offset': 0.002},
              'B14': {'slope': 1.02, 'offset': -0.18}}

filenames = glob.glob('*FLDK*.dat')
scene = satpy.Scene(filenames,
                    reader='ahi_hsd',
                    reader_kwargs={'user_calibration': calib_dict)
# B15 will not have custom radiance correction applied.
scene.load(['B07', 'B14', 'B15'])

By default, user-supplied calibrations / corrections are applied to the radiance data in accordance with the GSICS standard defined in the equation above. However, user-supplied gain and offset values for converting digital number into radiance via Rad = DN * gain + offset are also possible. To supply your own factors, supply a user calibration dict using type: ‘DN’ as follows:

calib_dict = {'B07': {'slope': 0.0037, 'offset': 18.5},
              'B14': {'slope': -0.002, 'offset': 22.8},
              'type': 'DN'}

You can also explicitly select radiance correction with ‘type’: ‘RAD’ but this is not necessary as it is the default option if you supply your own correction coefficients.

Initialize the reader.

property area

Get AreaDefinition representing this file’s data.

calibrate(data, calibration)[source]

Calibrate the data.

convert_to_radiance(data)[source]

Calibrate to radiance.

property end_time

Get the end time.

get_area_def(dsid)[source]

Get the area definition.

get_dataset(key, info)[source]

Get the dataset.

read_band(key, info)[source]

Read the data.

property scheduled_time

Time this band was scheduled to be recorded.

property start_time

Get the start time.