Remote Sensing Hands-On Lesson using BepiColombo MPO¶
Virtual SPICE Training for BepiColombo, July 21-22, 2020
Overview¶
In this lesson you will develop a series of simple programs that demonstrate the usage of SpiceyPy to compute a variety of different geometric quantities applicable to experiments carried out by a remote sensing instrument flown on an interplanetary spacecraft.
You may find it useful to consult the permuted index, the headers of various source modules, and several Required Reading documents available at the NAIF site.
Initialise SPICE by importing SpiceyPy¶
For the following exercises, instead of loading the meta-kernel try to sort out the exact kernels that you need to load for the given execrcise and load them (unless indicated).
import spiceypy
Time Conversion¶
Write a program that given a UTC time string, converts it to the following time systems and output formats:
- Ephemeris Time (ET) in seconds past J2000
- Calendar Ephemeris Time
- Spacecraft Clock Time (TIP: You will need to know the NAIF ID of MPO)
and displays the results. Use the program to convert "2020-OCT-15 03:57:49" UTC into these alternate systems.
#
# We need to load the leapseconds kernel and the SCLK kernel.
#
spiceypy.furnsh('../kernels/lsk/naif0012.tls')
spiceypy.furnsh('../kernels/sclk/bc_mpo_step_20200713.tsc')
et = spiceypy.utc2et('2020-10-15T03:57:49')
print(' Ephemeris Time (ET) in seconds past J2000: {}'.format(et))
calet = spiceypy.timout( et, 'YYYY-MON-DDTHR:MN:SC ::TDB' )
print( ' Calendar Ephemeris Time: {:s}'.format( calet ) )
#
# We will need the SCLK ID of MPO that we can retrieve from the SCLK file itself.
#
sclkid = -121
sclkst = spiceypy.sce2s( sclkid, et )
print( ' Spacecraft Clock Time: {:s}'.format( sclkst ) )
#
# We unload all the kernels in the kernel pool
#
spiceypy.kclear()
Obtaining Target States and Positions - Venus Flyby¶
Write a program that given a UTC time string computes the following quantities at that epoch:
The apparent state of Venus as seen from BepiColombo MPO in the J2000 frame, in kilometers and kilometers/second. This vector itself is not of any particular interest, but it is a useful intermediate quantity in some geometry calculations.
The one-way light time between BepiColombo MPO and the apparent position of Earth, in seconds.
The actual (geometric) distance between the Sun and Venus, in astronomical units.
and displays the results. Use the program to compute these quantities at "2020-OCT-15 03:57:49" UTC.
#
# We need to load the leapseconds kernel the Solar System ephemeris and the MPO SPK.
#
spiceypy.furnsh('../kernels/lsk/naif0012.tls')
spiceypy.furnsh('../kernels/spk/de432s_20201013_20201016.bsp')
spiceypy.furnsh('../kernels/spk/bc_mpo_fcp_Venus1SwingbyMTP_v01.bsp')
et = spiceypy.utc2et('2020-10-15T03:57:49')
#
# Compute the apparent state of Mercury as seen from BepiColombo MPO in the J2000 frame.
# All of the ephemeris readers return states in units of kilometers and km/s.
#
[state, ltime] = spiceypy.spkezr('VENUS', et,'J2000','LT+S','MPO' )
print( ' Apparent state of Venus as seen from BepiColombo MPO in the J2000\n'
' frame (km, km/s):')
print( ' X = {:16.3f}'.format(state[0]) )
print( ' Y = {:16.3f}'.format(state[1]) )
print( ' Z = {:16.3f}'.format(state[2]) )
print( ' VX = {:16.3f}'.format(state[3]) )
print( ' VY = {:16.3f}'.format(state[4]) )
print( ' VZ = {:16.3f}\n'.format(state[5]) )
#
# Compute the apparent position of Earth as seen from
# BepiColombo MPO in the J2000 frame.
#
[pos, ltime] = spiceypy.spkpos( 'EARTH', et, 'J2000', 'LT+S', 'MPO')
print( ' One way light time between BepiColombo MPO and the apparent\n'
' position of Earth: {} seconds\n'.format(ltime))
#
# Now we need to compute the actual distance between the Sun and Mercury.
# We need to adjust our aberration correction appropriately.
#
[pos, ltime] = spiceypy.spkpos( 'SUN', et, 'J2000','NONE', 'VENUS')
#
# Compute the distance between the body centers in kilometers.
#
dist = spiceypy.vnorm( pos )
#
# Convert this value to AU using convrt.
#
dist = spiceypy.convrt( dist, 'KM', 'AU' )
print( ' Actual distance between Sun and Venus body centers: {} AU'.format(dist))
spiceypy.kclear()
Spacecraft Orientation and Reference Frames¶
Write a program that given a UTC time string computes and displays the following at the epoch of interest:
- The angular separation between the apparent position of BepiColombo MMO as seen from BepiColombo MPO and the nominal instrument view direction.
The nominal instrument view direction is not provided by any kernel variable, but it is indicated in the BepiColombo MPO frame kernel.
Use the program to compute these quantities at the epoch "2027 JUN 11 20:50:00" UTC.
#
# Since we need orientation information in addition to the kernels we loaded before
# now we need to load the Frames Kernel, the SCLK kernel and the MPO CK kernel.
# It is also important to note that we need to load the frames kernel containing the
# MPO Science frames
#
spiceypy.furnsh('../kernels/lsk/naif0012.tls')
spiceypy.furnsh('../kernels/spk/de432s_20270609_20270614.bsp')
spiceypy.furnsh('../kernels/spk/bc_mpo_mlt_50037_20270609_20270614_v01.bsp')
spiceypy.furnsh('../kernels/spk/bc_mmo_mlt_50038_20270609_20270614_v01.bsp')
spiceypy.furnsh('../kernels/spk/bc_mpo_cog_v01.bsp')
spiceypy.furnsh('../kernels/sclk/bc_mpo_step_20200713.tsc')
spiceypy.furnsh('../kernels/ck/bc_mpo_sc_slt_50028_20270609_20270614_s20200713_v01.bc')
spiceypy.furnsh('../kernels/fk/bc_mpo_v23.tf')
spiceypy.furnsh('../kernels/fk/bc_sci_v06.tf')
et = spiceypy.utc2et('2027-06-11T20:50:00')
#
# We compute the apparent position of MMO as seen from
# MPO in the J2000 frame.
#
[pos, ltime] = spiceypy.spkpos('MMO',et,'J2000','LT+S','MPO')
[pos, ltime] = spiceypy.spkpos('MMO',et,'MPO_SPACECRAFT','LT+S','MPO')
#
# Now compute the location of the nominal instrument view
# direction. From reading the frame kernel we know that
# the instrument view direction is nominally the +Z axis
# of the TGO_SPACECRAFT frame defined there.
#
bsight = [ 0.0, 0.0, 1.0]
#
# Now compute the rotation matrix from MPO_SPACERAFT into
# J2000.
#
pform = spiceypy.pxform('MPO_SPACECRAFT','J2000', et )
#
# And multiply the result to obtain the nominal instrument
# view direction in the J2000 reference frame.
#
#bsight = spiceypy.mxv(pform, bsight)
#
# Lastly compute the angular separation.
#
sep = spiceypy.convrt(spiceypy.vsep(bsight, pos),'RADIANS','DEGREES')
print(' Angular separation between the apparent position of MMO and the\n'
' MPO nominal instrument view direction (degrees): {:.3f}'.format(sep))
spiceypy.kclear()
Computing Sub-s/c and Sub-solar Points on an Ellipsoid¶
Write a program that given a UTC time string computes the following quantities at that epoch:
- The apparent sub-observer point of MPO on Mercury, in the body fixed frame IAU_MERCURY, in kilometers.
- The apparent sub-solar point on Mercury, as seen from MPO in the body fixed frame IAU_MERCURY, in kilometers.
For the computations use the ellipsoidal shape model:
near point/ellipsoid
definition.
The program displays the results. Use the program to compute these quantities at "2027 JUN 11 20:10:00" UTC.
spiceypy.furnsh('../kernels/lsk/naif0012.tls')
spiceypy.furnsh('../kernels/spk/de432s_20270609_20270614.bsp')
spiceypy.furnsh('../kernels/spk/bc_mpo_mlt_50037_20270609_20270614_v01.bsp')
spiceypy.furnsh('../kernels/spk/bc_mmo_mlt_50038_20270609_20270614_v01.bsp')
spiceypy.furnsh('../kernels/spk/bc_mpo_cog_v01.bsp')
spiceypy.furnsh('../kernels/sclk/bc_mpo_step_20200713.tsc')
spiceypy.furnsh('../kernels/ck/bc_mpo_sc_slt_50028_20270609_20270614_s20200713_v01.bc')
spiceypy.furnsh('../kernels/fk/bc_mpo_v23.tf')
spiceypy.furnsh('../kernels/fk/bc_sci_v06.tf')
spiceypy.furnsh('../kernels/pck/pck00010.tpc')
et = spiceypy.utc2et('2027-06-11T20:10:00')
#
# Use the "near point" sub-point definition
# and an ellipsoidal model.
#
method = 'NEAR POINT/Ellipsoid'
#
# Compute the apparent sub-observer point of MPO on Mercury.
#
[spoint, trgepc, srfvec] = spiceypy.subpnt(method,'MERCURY',et,
'IAU_MERCURY','LT+S','MPO' )
print( ' Apparent sub-observer point of MPO on Mercury\n'
' in the IAU_MERCURY frame (km):' )
print( ' X = {:.3f}'.format(spoint[0]) )
print( ' Y = {:.3f}'.format(spoint[1]) )
print( ' Z = {:.3f}'.format(spoint[2]) )
print( ' ALT = {:.3f}\n'.format(spiceypy.vnorm(srfvec)) )
#
# Compute the apparent sub-solar point on Mercury as seen from MPO
#
[spoint, trgepc, srfvec] = spiceypy.subslr(method,'MERCURY',et,'IAU_MERCURY',
'LT+S','MPO' )
print( ' Apparent sub-solar point on Mercury as seen from MPO \n'
' in the IAU_MERCURY frame (km):' )
print( ' X = {:.3f}'.format(spoint[0]) )
print( ' Y = {:.3f}'.format(spoint[1]) )
print( ' Z = {:.3f}\n'.format(spoint[2]) )
#
# We unload all the kernels in the kernel pool
#
spiceypy.kclear()
Intersecting Vectors with an Ellipsoid (fovint)¶
Write a program given an input UTC time string that computes the intersection of the MPO SERENA ELENA
boresight and field of view (FOV) boundary vectors with the surface of Mercury.
The program presents each point of intersection as
- Planetocentric (latitudinal) coordinates in the IAU_MERCURY frame.
For each of the sensor FOV boundary and boresight vectors, if an intersection is found, the program displays the results of the above computations, otherwise it indicates no intersection exists.
At each point of intersection compute the following:
- Phase angle
- Solar incidence angle
- Emission angle
Use this program to compute values at "2027 JUN 11 20:10:00" UTC.
spiceypy.furnsh('../kernels/mk/bc_training_class.tm')
et = spiceypy.utc2et('2027-06-11T20:10:00')
#
# Now we need to obtain the FOV configuration of
# the SERENA ELENA aperture. To do this we will
# need the ID code for MPO_SERENA_ELENA.
#
lnonid = spiceypy.bodn2c('MPO_SERENA_ELENA')
#
# Now retrieve the field of view parameters.
#
[shape,insfrm,bsight,n,bounds ] = spiceypy.getfov(lnonid,4)
#
# `bounds' is a numpy array. We'll convert it to a list.
#
# Rather than treat BSIGHT as a separate vector,
# copy it into the last slot of BOUNDS.
#
bounds = bounds.tolist()
bounds.append( bsight )
#
# Set vector names to be used for output.
#
vecnam = [ 'Boundary Corner 1',
'Boundary Corner 2',
'Boundary Corner 3',
'Boundary Corner 4',
'MPO_SERENA_ELENA Boresight' ]
#
# Now perform the same set of calculations for each
# vector listed in the BOUNDS array.
#
for i in range(5):
#
# Call sincpt to determine coordinates of the
# intersection of this vector with the surface
# of Mercury.
#
print( ' Vector: {:s}\n'.format( vecnam[i] ) )
[point,trgepc,srfvec] = spiceypy.sincpt('ELLIPSOID','MERCURY',et,
'IAU_MERCURY', 'LT+S','MPO',
insfrm, bounds[i])
#
# Display the planetocentric latitude and longitude of the intercept.
#
[radius,lon,lat] = spiceypy.reclat( point )
print( ' Planetocentric coordinates of the intercept (degrees):')
print( ' LAT = {:.3f}'.format(lat * spiceypy.dpr() ) )
print( ' LON = {:.3f}\n'.format(lon * spiceypy.dpr() ) )
#
# Compute the illumination angles at this point.
#
[trgepc,srfvec,phase,solar,emissn, visibl,lit] = spiceypy.illumf(
'ELLIPSOID','MERCURY','SUN',et,'IAU_MERCURY',
'LT+S','MPO', point)
print( ' Phase angle (degrees): {:.3f}'.format(phase*spiceypy.dpr()))
print( ' Solar incidence angle (degrees): {:.3f}'.format(solar*spiceypy.dpr()))
print( ' Emission angle (degrees): {:.3f}'.format(emissn*spiceypy.dpr()))
print( ' Observer visible: {:s}'.format(str(visibl)))
print( ' Sun visible: {:s}\n'.format(str(lit)))
#
# End of vector loop.
#
spiceypy.kclear()
Extra Credit: Lessons with WGC¶
Try to reproduce all the previous calculations with WebGeocalc. You will need to load the appropriate meta-kernel: "SPICE CLASS -- BepiColombo Remote Sensing Lesson Kernels"