OSIRIS Level 1 Services

The osirisl1services.services module supplies users with an xarray accessor L1Services that supplies additional functionality for the computation of spatial positioning, pointing, and tangent point information through the accessor name l1.

Pointing

The accessor supports computation of instrument lines of sight or both the IR and spectrograph datasets in both ECEF and ECI coordinates:

• l1.look_ecef

• l1.look_eci

These pointing vectors are expressed as unit XYZ vectors in an earth centered inertial coordinate system. For the IR instrument, a look vector is computed for each pixel. For the spectrograph, a single look vector for each exposure.

Position and Velocity

The accessor supports the calculation of spacecraft position and velocity in both ECEF and ECI coordinates systems. This functionality is provided by the functions below and can be applied to the IR and spectrograph datasets:

• l1.position_ecef

• l1.position_eci

• l1.velocity_ecef

• l1.velocity_eci

Tangent Points

Using pointing and position methods in conjunction allows us to calculate the location of tangent points for each saltellite position / look vector pair. This is accessed via:

• l1.altitude

• l1.latitude

• l1.longitude

As with the pointing, the data is computed for each pixel for IR data and each exposure for spectrograph data.

Solar Angles

Additionally, the solar angles relative to the tangent point can be calculated. This is accessed via:

• l1.sza: the solar zenith angle

• l1.ssa: the solar scattering angle

• l1.saa: the solar azimuth angle

• l1.satellite_azimuth_angle: the azimuth angle of the satellite look vector

As with the pointing, the data is computed for each pixel for IR data and each exposure for spectrograph data.

Apparent Solar Time

The apparrent solar angles time is accessed via:

• l1.apparent_solar_time

Miscellaneous

Additional methods are available to compute the satellites position and velocity in ECEF and ECI coordinates for an arbitrary list of mjds rather than for a specific spectrograph scan or IR orbit:

• services.get_odin_position_ecef()

• services.get_odin_position_eci()

• services.get_odin_velocity_ecef()

• services.get_odin_velocity_eci()

The final method within the osirisl1services.services module is services.get_scans_in_orbit_below_sza(). As its name suggests, this function takes an orbit number and a value of solar zenith angle as input, and returns all scans within the specified orbit with solar zenith angles lower than the given angle.