Four of this mooring's instruments produced pressure records: three
MicroCats and an Aanderaa.
The initial rest pressure from the shallowest MicroCat is 388.7 db,
which corresponds to a depth of 385.4 meters. The only significant
change in rest depth occurred during 22-23 May, when the rest depth
increased by about 3 db.
However, the pressure record from the top Aanderaa shows no depth
change at all during May. The rest pressure, throughout most of the
record, varies from 380.9 db to 383.1 db, which is a change of just
one bit and is not significant. Both pressures are found before and
after the 22-23 May change observed elsewhere. Thus the rest pressure
in this record is remarkably constant. The lowest pressure recorded,
378.6 db, is one bit below 380.9 db and is present in only a few lines.
It is equivalent to a depth of 375.4 meters, which we could take as
an estimate for the rest depth of the instrument.
The next deeper instrument, a MicroCat, recorded an initial rest
pressure of 596.4 db, which corresponds to a depth of 591.1 meters.
The only significant change in rest pressure occurred during 22-23 May,
when the mooring appears to have moved about 4 meters deeper. (The rest
pressure increased from 597.1 db to 601.0 db).
The fourth pressure record from this mooring is from the MicroCat at an
nominal depth of 798 meters. The initial rest pressure was 790.8 db,
which corresponds to a depth of 783.4 meters. Like the other MicroCats,
this one experience a pressure increase on 22-23 May, from 791.5 db to
795.4 db.
Putting these figures together, we have (rounding to the nearest meter)
nominal depth measured depth difference
398 m 385 m 14 m
399 m 375 m 24 m
598 m 591 m 7 m
798 m 783 m 15 m
where measured depth is the initial measured depth.
This is not a consistant picture. It does seem, however, that the given
bottom depth, 999 meters, may be too deep. Possiby the best we can do
here is average the four differences shown above and subtract that average
from all the nominal depths. The average is 15 meters, so in this data
report we have taken the seafloor depth to be 999 - 15 = 984 meters, and
have adjusted the instrument depths accordingly. Thus the top MicroCat is
placed at 398 - 15 = 383 meters, the Aanderaa immediately below it at 384
meters, the next MicroCat at 583 meters, and so on.
Move up one level.