CL_op_latSwath

Description

• Computes the intersection of an instrument's swath with a parallel (small circle at a specified latitude) for a circular orbit and a spherical planet.

  The swath instrument outlines are formed by two beams in the plane perpendicular to the inertial velocity. Each beam is defined by a "center angle" (angc): angle from the planet center between the radius vector and the intersection of the beam with the planet. The angle is signed: negative to the left (direction of the angular momentum vector), and positive to the right.

  

  Two longitude intervals (lona and lond) are computed for the ascending and descending pass for one orbit (ascending node to the next). Times intervals (ta and td) when the swath crosses the longitude intervals are optionally computed. By convention, the spacecraft is supposed to be at longitude 0 and going from South to North at time 0.

  Additional information (info) is also returned:

  - nodper: The orbit's nodal period (s)

  - lgap: Longitude gap between two consecutive orbit tracks (rad)

  - ncase: situation encountered:

  0 = latitude not visible,

  1 = only one beam intersects the small circle at the specified latitude,

  2 = two beams intersect the small circle at the specified latitude,

  3 = latitude is visible from any orbit position in the orbit (polar case),

  4 = latitude is visible from any orbit position in the orbit (equatorial case)

• Notes:

  - Secular effect of J2 is taken into account.

  - Right ascension (rather than longitude) intervals can be computed by setting the rotation rate to 0.

Parameters

sma:

Semi major axis [m] (1xN or 1x1)

inc:

Inclination [rad] (1xN or 1x1)

angc:

Instrument's center angles [rad] (1xN or 1x1 or 2xN or 2x1)

lat:

Latitude [rad] (1xN or 1x1)

res:

type of output: "li" or "lti"

er:

(optional) Equatorial radius [m] (default is %CL_eqRad)

mu:

(optional) Gravitational constant [m^3/s^2] (default value is %CL_mu)

j2:

(optional) Zonal coefficient (second zonal harmonic) (default is %CL_j1jn(2))

rotr_pla:

(optional) Rotation rate of the planet [rad/s] (default is %CL_rotrBody)

lona:

Longitude interval for ascending pass [rad] (2xN)

lond:

Longitude interval for descending pass [rad] (2xN)

ta:

Time interval for ascending pass [s] (1xN)

td:

Time interval for descending pass [s] (1xN)

info:

(struct) Additional information - see above

Authors

• CNES - DCT/SB

See also

• CL_gm_visiParams

• CL_op_equatorialSwath

Examples

// Orbit (sma + inc) sma = 7.e6; // m inc = 60 * %pi/180; // rad // instrument center angles angc = [-1; 2] * %pi/180; // Latitude of interest lat = 40 * %pi/180; // Longitude intervals [lona, lond] = CL_op_latSwath(sma, inc, angc, lat) // Longitude and intervals and additional info [lona, lond, ta, td, info] = CL_op_latSwath(sma, inc, angc, lat, res="lti")