DISPHASE

Name

disphase

Purpose

Apply distance and phase angle correction to observed magnitudes.

Description

Apply standard asteroidal-law corrections to observed magnitudes
given the distance, phase angle, and the G coefficient. Magnitudes
are corrected to 1 AU from Sun and Earth and to 0 degrees phase angle.
The default of this routine is to use equation A4 from Bowell etal. in
Asteroids II (see page 550) and called the Lumme and Bowell model.
An option is provided to compute the IAU standard correction from
equation A5 found on page 551.
According to the Bowell chapter, these expressions are valid only
for 0<=G<=1 and phase angle less than 120 degrees. However, the
chapter also claims the expressions are useful outside this range.
Note that the computation blows up in single precision if G < -0.85. If
the input value for G is out of range then the returned magnitude is
set to -99.99. This prevents getting back a value of NaN for hmag.

Calling Sequence

disphase,mag,r,d,phang,g,hmag

Inputs

mag - Observed magnitude.
r - Sun-object distance in AU.
d - Earth-object distance in AU.
phang - Phase angle of observation in degrees.
g - IAU standard G value (phase angle coefficient).

Optional Input Parameters

Keyword Input Parameters

H2MAG - Flag, if set reverses the sense of the calculations and takes
H as the input magnitude and then computes the apparent
magnitude for the output.
IAU - Flag, if set will force the use of the lower accuracy IAU
standard calculation. The default is to use the
Lumme and Bowell model.

Outputs

hmag - Magnitude corrected for distance and phase angle.

Keyword Output Parameters

Common Blocks

Side Effects

Restrictions

Procedure

Modification History

2008/04/12, MWB, slight change to deal with bogus values for G
2016/01/06, MWB, added H2MAG keyword option
2016/01/13, MWB, added IAU keyword option