Solar system objects move across the image during an exposure. If the movement is significant, the signal to noise ratio of the object decreases compared to an equivalent stationary object.
def trailing_losses(velocity, seeing, texp=30.):
"""Calculate detection-based and SNR-based trailing losses.
Parameters
==========
velocity : float
The velocity of the moving object, in deg/day.
seeing : float
The seeing in the image, in arcseconds.
texp : float, opt
The exposure time, in seconds.
Returns
=======
dict
dmag['trail'] and dmag['detect'] - detection and SNR losses.
"""
a_trail = 0.761
b_trail = 1.162
a_det = 0.420
b_det = 0.003
x = velocity * texp / seeing / 24.0
dmag = {}
dmag['trail'] = 1.25 * np.log10(1 + a_trail*x**2/(1+b_trail*x))
dmag['detect'] = 1.25 * np.log10(1 + a_det*x**2 / (1+b_det*x))
return dmag
Note
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Calculating trailing losses for moving objects.