How to use the pyorbital.astronomy.cos_zen function in pyorbital

'''

        try:
            from pyorbital import astronomy
        except ImportError:
            LOG.warning("Could not load pyorbital.astronomy")
            return None

        if lons is None or lats is None:
            # Read coordinates
            lons, lats = self.area.get_lonlats()
    
        # Calculate Sun zenith angles and the cosine
        zen_angles = astronomy.sun_zenith_angle(time_slot, 
                                                lons, lats)
        cos_zen = astronomy.cos_zen(time_slot, lons, lats)

        # Copy the channel
        new_ch = copy.deepcopy(self)
        # Update the name
        if name is None:
            new_ch.name += '_SZC'
        else:
            new_ch.name = name

        if mode == 'cos':
            # Cosine correction
            lim_y, lim_x = np.where(zen_angles < limit)
            new_ch.data[lim_y, lim_x] /= cos_zen[lim_y, lim_x]
            # Use constant value (the limit) for larger zenith
            # angles
            lim_y, lim_x = np.where(zen_angles >= limit)

try:
            from pyorbital import astronomy
        except ImportError:
            LOG.warning("Could not load pyorbital.astronomy")
            return None

        if lonlats is None or len(lonlats) != 2:
            # Read coordinates
            LOG.debug("No valid coordinates given, reading from the "
                      "channel data")
            lons, lats = self.area.get_lonlats()
        else:
            lons, lats = lonlats

        # Calculate Sun zenith angles and the cosine
        cos_zen = astronomy.cos_zen(time_slot, lons, lats)

        # Copy the channel
        new_ch = copy.deepcopy(self)

        # Set the name
        new_ch.name += '_SZC'

        if mode == 'cos':
            new_ch.data = mpop.tools.sunzen_corr_cos(new_ch.data,
                                                     cos_zen, limit=limit)
        else:
            # Placeholder for other correction methods
            pass

        # Add information about the corrected version to original
        # channel

try:
            from pyorbital import astronomy
        except ImportError:
            LOG.warning("Could not load pyorbital.astronomy")
            return None

        if lonlats is None or len(lonlats) != 2:
            # Read coordinates
            LOG.debug("No valid coordinates given, reading from the "
                      "channel data")
            lons, lats = self.area.get_lonlats()
        else:
            lons, lats = lonlats

        # Calculate Sun zenith angles and the cosine
        cos_zen = astronomy.cos_zen(time_slot, lons, lats)

        # Copy the channel
        new_ch = copy.deepcopy(self)

        # Set the name
        new_ch.name += '_SZC'

        if mode == 'cos':
            new_ch.data = satpy.tools.sunzen_corr_cos(new_ch.data,
                                                      cos_zen, limit=limit)
        else:
            # Placeholder for other correction methods
            pass

        # Add information about the corrected version to original
        # channel

if hasattr(vis.attrs["area"], 'name'):
            area_name = vis.attrs["area"].name
        else:
            area_name = 'swath' + str(vis.shape)
        key = (vis.attrs["start_time"], area_name)
        tic = time.time()
        LOG.debug("Applying sun zen correction")
        if len(projectables) == 1:
            coszen = self.coszen.get(key)
            if coszen is None:
                from pyorbital.astronomy import cos_zen
                LOG.debug("Computing sun zenith angles.")
                lons, lats = vis.attrs["area"].get_lonlats_dask(CHUNK_SIZE)

                coszen = xr.DataArray(cos_zen(vis.attrs["start_time"],
                                              lons, lats),
                                      dims=['y', 'x'],
                                      coords=[vis['y'], vis['x']])
                coszen = coszen.where((coszen > 0.035) & (coszen < 1))
                self.coszen[key] = coszen
        else:
            coszen = np.cos(np.deg2rad(projectables[1]))
            self.coszen[key] = coszen

        if vis.shape != coszen.shape:
            # assume we were given lower resolution szen data than band data
            LOG.debug(
                "Interpolating coszen calculations for higher resolution band")
            factor = int(vis.shape[1] / coszen.shape[1])
            coszen = np.repeat(
                np.repeat(coszen, factor, axis=0), factor, axis=1)

area_name = hash(vis.attrs['area'])
        key = (vis.attrs["start_time"], area_name)
        tic = time.time()
        LOG.debug("Applying sun zen correction")
        coszen = self.coszen.get(key)
        if coszen is None and len(projectables) == 1:
            # we were not given SZA, generate SZA then calculate cos(SZA)
            from pyorbital.astronomy import cos_zen
            LOG.debug("Computing sun zenith angles.")
            lons, lats = vis.attrs["area"].get_lonlats(chunks=CHUNK_SIZE)

            coords = {}
            if 'y' in vis.coords and 'x' in vis.coords:
                coords['y'] = vis['y']
                coords['x'] = vis['x']
            coszen = xr.DataArray(cos_zen(vis.attrs["start_time"], lons, lats),
                                  dims=['y', 'x'], coords=coords)
            if self.max_sza is not None:
                coszen = coszen.where(coszen >= self.max_sza_cos)
            self.coszen[key] = coszen
        elif coszen is None:
            # we were given the SZA, calculate the cos(SZA)
            coszen = np.cos(np.deg2rad(projectables[1]))
            self.coszen[key] = coszen

        proj = self._apply_correction(vis, coszen)
        proj.attrs = vis.attrs.copy()
        self.apply_modifier_info(vis, proj)
        LOG.debug("Sun-zenith correction applied. Computation time: %5.1f (sec)", time.time() - tic)
        return proj