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The laser altimeter's synchronized recording of exposure station 
to lunar surface distance with a rated 1-2 meter accuracy, provides 
an unusual data contribution to the photogrammetric solution. The 
laser energy reflected from the lunar surface is not sufficient to 
be imaged on the accompanying terrain photograph and identification 
of point of reflectance is dependent on recovery of a calibrated 
position located some 60 micrometers from the photo principal point. 
Incorporation of the laser altimeter point in the triangulation 
requires identification and photographic transfer of this ill 
defined image. Also, a small error in determining photographic 
location in an area of significant slope will affect the reliability 
of the photogrammetric determination of distance to exposure 
station. Considering these limitations and the capability of 
deriving ground coordinates to a 20 meters accuracy implied by the 
precision achieved in attitude determination and relative triangu- 
lation; it would appear that the laser altimeter will principally 
contribute to the triangulation by enabling identification and 
diagnosis of the presence and cause of systematic error. The laser 
altimeter was operative for only a portion of Apollo 15's orbital 
photographic mission. Within the test area, altimeter recordings 
are available for all seven frames on revolution 22 and three 
frames of revolution 29. On revolution 22 agreement to a 10 meter 
level was achieved between photogrammetric and laser altimeter 
determinations of exposure station height above the lunar surface. 
Comparison of revolution 27 results showed a largely systematic 
difference of 50 meters. 
The spacecraft ephemeris definition of exposure station position 
is provided by the position and velocity components of the state 
vector expressed for each instant of exposure. Timing information 
affords the means for relating metric camera system results to the 
defined orbital positions. The validity of the positions are them- 
selves dependent on timed earthbased radar observations and 
knowledge of the relative motions of the moon and earth during the 
observation period. Considering the rated +1 millisecond accuracy 
of exposure to spacecraft ephemeris time for a single orbital 
revolution and a nominal spacecraft velocity of 1600 meters/second, 
an error of 1.6 meters would be present in individual exposure 
station positions due to timing inaccuracy. The relative accuracy 
of timing information between orbital revolutions is 5 milliseconds, 
implying exposure station errors of 8 meters in relating adjacent 
photographic strips. Other more significant expected sources of 
error in the spacecraft ephemeris definition of exposure station 
position, are orbital perturbations caused by unmodeled lunar 
gravity anomalies and errors due to imprecision in our knowledge of 
the moon's motion. The former would appear to be more susceptible 
to definition in Apollo 15 photogrammetric solutions where photog- 
raphy was acquired during a relatively short time period.