How to get sat/solar zenith and solar reflection angles from GOES16 data?

[Paulo Victorino]

Hello pytroll community.

Anyone knows how to get satellite/solar zenith angles and solar reflection angle from GOES 16 raw data?

I'm using the pytroll to detect fire on GOES 16 data, but I couldn't identify which module I could used to get the angles.

Thanks for help.

Victorino

[Martin Raspaud]

Hi Paulo,

You should be able to use pyorbital for this. I'm not sure what you call solar reflection angle (is it the azimuth difference ?), but the zenith angles you can definitely get from pyorbital.

Best regards,

Martin

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Martin Raspaud, PhD

Software engineer

SMHI, SE-60176

[Diego Souza]

Hi Paulo, 

This is what I do:

# Satellite height
sat_h = file4.variables['goes_imager_projection'].perspective_point_height
# Satellite longitude
sat_lon = file4.variables['goes_imager_projection'].longitude_of_projection_origin
# Satellite sweep
sat_sweep = file4.variables['goes_imager_projection'].sweep_angle_axis
# The projection x and y coordinates equals
# the scanning angle (in radians) multiplied by the satellite height (http://proj4.org/projections/geos.html)
X = file4.variables['x'][:][::1] * sat_h
Y = file4.variables['y'][:][::1] * sat_h
# map object with pyproj
p = Proj(proj='geos', h=sat_h, lon_0=sat_lon, sweep=sat_sweep, a=6378137.0)
# Convert map points to latitude and longitude with the magic provided by Pyproj
XX, YY = np.meshgrid(X, Y)
lons, lats = p(XX, YY, inverse=True)

utc_time = datetime(2018, 9, 5, 22, 30)
sun_zenith = np.zeros((data4.shape[0], data4.shape[1]))
sun_zenith = astronomy.sun_zenith_angle(utc_time, lons, lats)

[David Hoese]

Hi Paulo,

As Martin mentioned this can be done with pyorbital. It is something
that will eventually be automatic in SatPy but right now is limited to
an internal process of generating composites. You could perform the same
calculations the composites are using here and copying it to your own
function:
https://github.com/pytroll/satpy/blob/master/satpy/composites/__init__.py#L387

So your example code might look like:

from satpy import Scene
scn = Scene(reader='abi_l1b', filenames=filenames)
scn.load(['C02']) # where you load whatever channel you want
angles for
sata, satz, suna, sunz = get_angles(scn['C02'])

Note that the results of this are dask arrays and not xarray DataArrays.
If you'd like to convert these to DataArrays let me know otherwise
`sata.compute()` will compute them and give you a numpy array.

If you have any further questions (I know it has been a while since you
originally asked this question) feel free to reply here, create a github
issue, or join our slack team for quicker responses.

Dave

On 9/25/18 1:32 PM, Diego Souza wrote:
> Hi Paulo,
>
> This is what I do:
>
> |
> # Satellite height

> sat_h =file4.variables['goes_imager_projection'].perspective_point_height
> # Satellite longitude
> sat_lon
> =file4.variables['goes_imager_projection'].longitude_of_projection_origin
> # Satellite sweep
> sat_sweep =file4.variables['goes_imager_projection'].sweep_angle_axis

> # The projection x and y coordinates equals
> # the scanning angle (in radians) multiplied by the satellite height
> (http://proj4.org/projections/geos.html)
> X =file4.variables['x'][:][::1]*sat_h
> Y =file4.variables['y'][:][::1]*sat_h
> # map object with pyproj
> p =Proj(proj='geos',h=sat_h,lon_0=sat_lon,sweep=sat_sweep,a=6378137.0)
> # Convert map points to latitude and longitude with the magic provided
> by Pyproj
> XX,YY =np.meshgrid(X,Y)
> lons,lats =p(XX,YY,inverse=True)
>
> utc_time =datetime(2018,9,5,22,30)
> sun_zenith =np.zeros((data4.shape[0],data4.shape[1]))
> sun_zenith =astronomy.sun_zenith_angle(utc_time,lons,lats)
> |
>
>
>
> On Thursday, March 8, 2018 at 11:28:40 AM UTC-3, Paulo Victorino wrote:
>
> Hello pytroll community.
>
> Anyone knows how to get satellite/solar zenith angles and solar
> reflection angle from GOES 16 raw data?
>
> I'm using the pytroll to detect fire on GOES 16 data, but I couldn't
> identify which module I could used to get the angles.
>
> Thanks for help.
> Victorino
>

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