CL_gm_visiParams

Description

• Computes various visibility parameters:

  - satellite's semi view-angle (sat): angle between the descending vertical and the direction of the target location

  - satellite's elevation (elev): elevation of the satellite as seen from the target location

  - satellite's incidence (incid = pi/2 - elev): incidence of the target-satellite direction from the target location

  - distance (dist): distance between the satellite and the target location

  - centre angle (cen): angle between the (body centre -> satellite) direction and the (body centre -> target location) direction.

  Given the distance from the body centre to the satellite (sat_radius), the distance from the body centre to the target (target_radius) and one of the following parameters (type_par1):

  - type_par1 = 'sat' , par1 = satellite's semi view angle.

  - type_par1 = 'elev' , par1 = elevation from the target location.

  - type_par1 = 'incid' , par1 = incidence (=pi/2-elev) from the target location.

  - type_par1 = 'dist' , par1 = distance between the target location and the satellite.

  - type_par1 = 'cen' , par1 = centre angle: angle from the body centre between the target location and the satellite.

  the function computes par2 whose type is defined by type_par2.

  type_par2 can also be an array of strings (any of the 5 parameters above), or 'all' and in that case the result is a structure whose fields are the 5 parameters above

  

• Notes:

  - A spherical body is assumed.

  - The function works even if "target_radius" is greater then "sat_radius".

  - If the input parameter is 'sat', 'elev" or "incid", there may be two solutions. Only one is computed, it corresponds to the smallest value of the centre angle.

Parameters

sat_radius:

Distance from the satellite to the body centre [m] (Px1 or PxN)

target_radius:

Distance from the target to the body centre [m] (Px1 or PxN)

type_par1:

(string) Type of input parameter 'par1'. It can be 'sat', 'elev', 'incid', 'dist', 'cen'

par1:

Satellite's semi view angle, elevation, indicence, distance or centre angle [rad,m] (Px1 or PxN)

type_par2:

(string) Type of output parameter: 'sat', 'elev', 'incid', 'dist', 'cen' or a vector containing any of them, or 'all'.

par2:

output parameter(s). Structure if type_par2 == "all". [rad,m] (PxN)

Authors

• CNES - DCT/SB

Examples

eqRad = CL_dataGet("eqRad"); sat_r = eqRad + 700.e3; // 700 km altitude target_r = eqRad + 0; // Ground // Distance to Ground incidence: [incid]=CL_gm_visiParams(sat_r,target_r,'dist',800.e3,'incid') // Satellite view angle to Ground elevation: [elev]=CL_gm_visiParams(sat_r,target_r,'sat',CL_deg2rad(10),'elev') // Centre angle to distance: [dist]=CL_gm_visiParams(sat_r,target_r,'cen',CL_deg2rad(7),'dist') // Ground incidence to satellite view angle and distance: [sat,dist]=CL_gm_visiParams(sat_r,target_r,'incid',CL_deg2rad(15),['sat','dist']) // Satellite view angle to everything: [result]=CL_gm_visiParams(sat_r,target_r,'sat',CL_deg2rad(37),'all');