HOLMES & NARVER, !nc.
ENGINEERS-CONSTRUCTORS
TO:
S. P. Howell
__JOB:
942
FROM:
Le Se Hammond
_Re.
Precise Surveys BikiniAtoli
Page 3
oaTe:__July 31, 1957
operation, the rodman loosens the target while the levelman throws
the bubble off center. After a lapse of a few minutes, in order
to allow a change in atmospheric conditions, the operation is
repeated.
This operation is repeated until a set of ten observa-~-
tions is secured.
At no time during the distant rod observations
may the focus of the telescope be changed.
The level is then moved carefully to the opposite end of the line
where it is set up approximately twenty feet from the other bench
mark and a set of ten reciprocal observations is taken on the
distant rod.
The level should be transported as rapidly as
possible so that atmospheric conditions during the two sets of the
observations will be the same, or similar and, in such a manner
that the focus of the telescope and the adjustment of the level
bubble are not changed. To ascertain that the focus of the telescope
is the same for both sets of distant observations, the distant tar-
get upon the latter set up is read before the rear rod is observed.
The mean difference determined by the two sets will be free from
the effect of level error, curvature and refraction if the atmospheric conditions are the same for both sets.
The mean value for the target observations is computed before the
instrument is moved, so that doubtful observations may be rejected
and replaced by new observations.
This entire operation is repeated across each stretch of water and
connected by first order leveling across the land areas between
bench marks.
The primary bench mark on NAN, established by tide gage observations,
becomes the datum for the operation. First order leveling is
accomplished between the primary bench mark and the new mark at the
north end of NAN, and from the new mark at the south end of HOW to
the scientific station locations on HOW.
As this program will require considerable time for scheduling and
field work it is recommended that the proposed program be submitted
to the jobsite for early reconnaissance and comments.
If adopted,
requisitions should be initiated for procurement of the required
equipment.
LSH/hg
ec:
D. ¢. VanDdins
Bngineering Files ~~.
L. S- Hammond