SCIENCE OVERVIEW:
This project involved onshore-offshore seismic profiling of the
crustal structure in the greater Los Angeles area, to identify and better
understand the earthquake hazards of the region. The Ewing served as a source
of seismic energy for both multichannel seismic reflection profiling as well as
for an dense array of land stations. Three main lines were run: one through the
Sierra Madre epicenter and Los Angeles Basin, one through the epicenter of the
Northridge earthquake, and a third trending NE-SW through the Los Angeles
basin.
TRUE TIME CLOCK:
Instrument: Kinemetric/TrueTime Division Model GPS-DC GPS Synchronized Clock
Logging: 1 minute intervals
NOTE: The True Time clock is used to adjust the CPU clock of the logging
computer. The logging computer captures the continuous time records from the
clock and provides these as a service to the rest of the network via a UDP
broadcast. This enables the computers on the network to adjust their CPU times
to UTC time.
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
start of cruise, started logging/processing
|
294
|
1600
|
end of cruise; stopped logging/processing
|
SPEED AND HEADING:
Instrument: Furuno CI-30 2-axis Doppler speed log, Sperry MK-27
gyro
Logging: 3 second intervals
Checking: visual check of plot of data
Smoothing: mean value of all good values within the same minute
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
start of cruise, started logging/processing
|
294
|
1600
|
end of cruise; stopped logging/processing
|
TRANSIT SATELLITE FIXES:
Instrument: Magnavox MX-1107RS dual frequency Transit satellite
receiver
Logging: all fixes
Checking: reject receiver flagged fixes, fixes with high drifts in
navigation
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
start of cruise, started logging/processing
|
294
|
1600
|
end of cruise; stopped logging/processing
|
GPS SATELLITE FIXES:
Instrument: Magnavox MX-4200 Global Positioning System receiver
Logging: 10 second intervals on GPS MX-4200 #1
10 second intervals on GPS MX-4200 #2
Checking:
minimum number of SATs: 3
dilution of precision maximum: north = 4.0, east = 4.0
carrier signal-noise ratio minimum: 35.0
standard deviation maximum: north =4.0, east = 4.0
time step maximum: 3
speed maximum: 30.0
compared GPS speed and course with Furuno smooth speed and heading
compared positions with Transit-Furuno navigation
reject fixes with high drifts in navigation
reject fixes producing Eotvos correction errors in gravity larger than 5
mGals
Interpolation: interpolated positions at 00, 30 seconds of each minute
Smoothing: smoothed interpolated positions with 9 or 41 point running
average depending on the quality of GPS data and the sea state.
Note:
The GPS data has a sinusoidal wave which is assumed to come from some degrading
of the GPS quality for civilian usage. This wave seems to vary in period and
shapes and is not a perfect sine curve. The periods are less than 20 minutes.
The amplitudes tend to vary over 24 hours and the sea state condition. This
degrading produces a false ship's track in real-time navigation and introduces
extreme errors, up to 10 mGals, in the Eotvos correction for the gravity. As
this problem varies in its intensit y depending on the sea state and GPS data
quality itself, several methods of data reduction has been developed to achieve
the best possible navigation.
1. A 9 point (4 minutes) GPS smoothing
2. A 9 point (4 minutes) GPS smoothing, decimated to a 20 min. fixes
3. A 41 point (20 minutes) GPS smoothing
4. A 41 point (20 minutes) GPS smoothing, decimated to a 20 min. fixes
It should be noted that the use of 41 point smoothing causes the turn to
"widens". Hence, in the instances where a 41 point smoothing is called for, the
GPS data at and around the turn are decimated to 20 minutes.
Throughout this cruise, a 9 point (4 minutes) GPS smoothing, decimated to a 20
min. fixes were used to produce final navigation data.
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
started data logging/processing
|
294
|
1600
|
end of cruise; stopped data logging/processing
|
NAVIGATION:
A "1 minute navigation" is produced from the above sources, which in this
cruise is a 9 point (4 minutes) GPS smoothing, decimated to a 20 min. fixes.
Acceptable fixes are merged at 1 per minute with priority given to GPS. The
smooth speed and heading dat a is used to fill any gaps of 2 minutes or longer
between fixes by computing 1 minute DR'ed positions corrected for set and drift
between fixes. The DR'ed positions are produced at 00 seconds of each minute.
Chief scientist's final data: 1 minute navigation.
FORMAT: n.ddd
yy+ddd:hh:mm:ss.mmm N 12 12.1234 E 123 12.1234 id 123.1 12.1
yr.day
time
lat.
lon
id set drift
Lamont database: 1 minute navigation, in MGG format.
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
started data processing
|
294
|
1600
|
end of cruise; stopped data processing
|
SEA TEMPERATURE:
Instrument: Omega DP10 Series
Logging: 1 minute intervals
Checking: none
Smoothing: none
Chief scientist's final data: one minute data, merged with navigation.
Lamont database: one minute data, merged with navigation.
FORMAT: ct.nddd
yy+ddd:hh:mm:ss:mmm N 12 12.1234 E 123.1234 26.3
yr day
time
lat
lon
sea_temp (in oC)
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
started data processing
|
294
|
1600
|
end of cruise; stopped data processing
|
MAGNETIC:
Instrument: Varian V75 magnetometer
Logging: 6 second intervals
Checking: visual check of plot of data
Reference field: International Geomagnetic Reference Field 1990
( IGRF 1990 ) model
of the main field at 1985.0 and a predictive model of
the secular variation
for adjusting to dates between 1990.0 and 1995.0.
Residual field: Applied by bi-linear interpolation across a 1 degree
square.
Chief Scientist's final data: final calibrated and cleaned data.
FORMAT: mg.nddd
yr+ddd:hh:mm:ss.mmm N 12 12.1234 E 123 12.1234 41200.8 -367.1
yr. day
time
lat
lon
total_intensity anomaly
Lamont Database: interpolated total intensity value at 00 second of each
minute
NOTE:
DAY
|
TIME
|
COMMENTS
|
286
|
2000
|
started logging
|
291
|
1624-2359
|
maggie off the water; no data
|
292
|
0000-0533
|
maggie off the water; no data
|
292
|
1710-2003
|
bad maggie data; data removed
|
294
|
0440
|
maggie off the water; end of logging
|
ADCP (Acoustic Doppler Current Profilers):
Instrument: RD Instrument RD-VM Model ADCP
Logging: logging is done by a 386 IBM PC compatible
Checking: none
Smoothing: none
Chief scientist's final data: processed data file format and navigation data
file format.
Lamont database: processed data file format and navigation data file format.
FORMAT: Refer to Transect User's Manual for Narrowband ADCP Appendix B.
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
beginning of the cruise; started logging/processing
|
294
|
1600
|
end of cruise; stopped logging/processing
|
BATHYMETRY:
Instrument: Krupp Atlas Hydrosweep Center Beam
Logging: At each ping of Hydrosweep, data is being broadcasted
real time to
the network, which is received by data logger. The logger computer then
extracted the center beam depth.
Checking: Visual checking aided by graphic editor to remove major
spikes.
Chief scientist's final data: final calibrated and cleaned center beam data,
two
nearest point to the minute interpolated to even minute.
Merged with final navigation.
Depth is in meters.
FORMAT: hb.nddd
yy+ddd:hh:mm:ss:mmm N 12 12.1234 E 123 12.1234 2222.0
yr.day
time
lat.
lon
depth_in_meters
Lamont database: final calibrated and cleaned data, interpolated to even
minute.
Merged with final navigation. MGG format.
Depth is in fathoms.
NOTE: At the beginning of EW-9414, a problem was found with the swath data
coming out of the Hydrosweep to the logging computer "olive". An "Unknown data
type" error message appeared in "get_hs" log file. Upon closer inspection, this
message was generated because the data coming out of the serial line seems to
be mangled if it happens to coincide with the pop of the seismic guns. It has
yet to be determined whether this was caused by the shock of the guns, or it
was an acoustic-interference problem.
DAY
|
TIME
|
COMMENTS
|
286
|
1520
|
started logging/processing
|
291
|
0104-0542
|
Hydrosweep was shut off to trace missing data problem
|
291
|
0837-0856
|
Hydrosweep was shut off to trace missing data problem
|
294
|
1600
|
end of cruise; stopped logging/processing
|
SHOT TIME & GUN DEPTH:
Instrument: L-DEO Time Tagger and GunDepth Interface
Logging: Shot Time from the Time tagger. Gun Depth from Gun Depth
Interface
FORMAT: ts.nddd (shot time)
94+173:00:04:04.333 000172 N 40 56.5884 W 125 42.6913 mcs-6a
SHOT TIME
shotnum
lat
lon
line name
FORMAT: dg.rddd (gun depth)
94+173:00:04:04.333 13 13 13 13 13 13 13 13 ....
SHOT TIME
GUN DEPTH
Note:
A '-' sign following the year means that shottime was not received in time. A
CPU timetag is placed instead. This sometimes happens at the beginning of the
line when the computer and the DMS-2000 are trying to get in sync with each
other. No gun was fired, and no data is recorded to the tape.
JDAY & TIME
|
Shot Number
|
LINE NAME
|
COMMENTS
|
286:18:49:17-287:05:41:37
287:11:55:42-288:01:24:01
288:01:28:30-288:06:32:37
288:06:32:56-288:12:35:17
288:12:36:27-288:21:44:45
288:21:45:16-289:12:10:24
289:12:11:30-290:02:37:25
290:02:38:46-290:04:59:09
290:05:17:27-291:02:54:01
291:01:54:58-291:19:56:51
291:20:52:55-292:04:04:19
292:04:05:21-292:12:31:41
292:13:29:27-292:17:50:16
292:17:51:16-292:23:49:10
292:23:51:10-293:06:40:04
293:06:40:41-293:13:56:16
293:14:00:13-293:14:43:08
293:14:43:08-293:16:44:02
293:18:35:45-294:04:31:30
|
0101-0753
0105-2414
0101-0935
0101-1068
0101-0783
0101-2546
0101-2587
0101-0494
0101-3215
0101-0822
0101-1369
0101-1619
0101-0883
0101-1174
0101-1327
0101-1407
0101-0126
0101-0462
0101-1885
|
LA01
LARSE01R
LARSE01X
LARSE01Y
LARSETR1
LARSE03
LARSE03R
LARSETR2
LARSE02
LARSE02R
LARSE02X
LARSE02Y
LARSE02Z
LARSETR3
LARSE01A
LARSE01B
LARSE04
MARSE04
LARSE06
|
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-time 90 secs.
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
|
Partial CO2:
Instrument: L-DEO PCO2 Group PCO2 Analysis Instrument
Logging: as is.
Checking: none
Chief scientist's final data: none.
Lamont database: merged data with final navigation.
FORMAT:
94+036:22:35:00.000 S 21 31.0624 W 31 27.2926 94036.9360
Yr Day Hr Mn Second
Lat
Lon
YrDay.frac
2033.8 2033.8 1014.0 34.64 33.8 419.9 404.5 28.41 Equil 28.2
IR_1 IR_2 Baro CellT Flow VCO2 pCO2 Eq_T Type SeaT
YrDay.frac
|
= Time of analysis
|
IR_1
|
= CO2 signal (mv)
|
IR_2
|
= CO2 signal (mv)
|
Baro
|
= IR Cell pressure (mbar)
|
CellT
|
= IR Cell temperature (deg C)
|
Flow
|
= Sample/Standard gas flow rate through IR cell (ml/mn)
|
VCO2
|
= Concentration of CO2 in dry gas sample (preliminary value) (ppm)
|
pCO2
|
= Partial pressure of CO2 in water-saturated air at temperature
of equilibration (uatm); (or residual of 2nd order fit if standard
(calibration) gas)
|
Eq_T
|
= Equilibration temperature (deg C)
|
Type
|
= Type of analysis [Equil= equilibrated seawater,
Airi= atmospheric air, Stdn= calibration gas]
|
SeaT
|
= Sea Surface Temperature, measured using thermistor on ship's
keel (depth= ?? meters) (deg C)
|
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
beginning of the cruise; started logging/processing
|
294
|
1600
|
end of cruise; stopped logging
|
WEATHER STATION:
Instrument: R.M/. Young Precision Meteorological Instruments 26700
Series
Logging: 1 minute interval
Checking: none
Chief scientist's final data: as is.
Lamont database: as is.
FORMAT: wx.rddd
Port bird is bird #1; starboard bird is bird #2.
94+022:00:00:00.244 9.3 15.4 13.2 21.1 271 261
date time wsi1 wss1 wsm1 wsx1 wdc1 wds1
6 12.6 15.9 15.6 20.7 261 253 6 66.7 66.7
wdm1 wsi2 wss2 wsm2 wsx2 wdc2 wds2 wdm2 tcur tavg
66.5 67.0 66 58 68 1016.8
tmin tmax rh rhn rhx baro
wsi1/2 = wind speed, instantaneous, bird #1/#2
wss1/2 = wind speed, 60 second average, bird #1/#2
wsm1/2 = wind speed, 60 minute average, bird #1/#2
wsx1/2 = wind speed, 60 minute maximum, bird #1/#2
wdc1/2 = wind direction, current, bird #1/#2
wds1/2 = wind direction, 60 second average, bird #1/#2
wdm1/2 = wind direction, 60 minute average, bird #1/#2
tcur = temperature, current
tavg = temperature, 60 minute average
tmin = temperature, 60 minute minimun
tmax = temperature, 60 minute maximum
rh = relative humidity
rhn = relative humidity, 60 minute minimum
rhx = relative humidity, 60 minute maximum
baro = barometric pressure
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
beginning of the cruise; started logging
|
294
|
1600
|
end of cruise; stopped logging
|
KSS-30 GRAVITY:
Instrument: Bodenseewerke KSS-30 marine gravity meter
Logging: 6 second intervals
Merge with navigation: calculate Eotvos correction and Free Air
Anomaly.
Checking: Visual check of plot of data to determine satisfactory Eotvos
corrections, reject spikes of data at turns.
Velocity smoothing: 5 point running average throughout the cruise
Processing:
The KSS-30 times tag is first adjusted for the filtering delay. For "Seastate"
setting 2, the delay due to filtering is 75 seconds. Thus75 seconds are
subtracted from the time tag and a new, adjusted time is computed.
A smooth KSS-30 gravity mgal value at one minute interval is calculated on 00
second of the minute by computing the unweighted mean values from the raw
values that lie between +-30 seconds of 00 seconds of the minute.
Calculation:
eotvos_corr = 7.5038 * vel_east * cos(lat) + .004154 * vel*vel
corrected_grv = raw_grv + eotvos_corr - drift - dc_shift
faa = corrected_grv - theoretical_grv
Chief scientist's final data: Observed, Eotvos, Free Air Anomaly value at 00
seconds of each minute.
1980 theoretical gravity formula:
Y0= 978.0327 x ( 1 + .0053024 x sin( Q ) x sin( Q ) -
.0000058 x sin( 2 x Q ) x sin( 2 x Q ) )
FORMAT: vk.nddd
yy+ddd:hh:mm:ss.mmm N 10 20.1234 W 120 23.1234 1980 77.1
yr. day
time
lat.
lon.
theog FAA
979317.5 64.1 1.5 10.2 -1.7 9.7 -1.6 9.8
raw_grav eotvos drift dc_shift raw_vel smo_vel
Lamont database: Free Air Anomaly value at 00 seconds of each minute.
1930 International gravity formula.
Note:
A '-' sign after the year in the record signifies a flagged record due to turn.
As a result of the discussion among the MG&G group, Lamont Data Reduction
will use Port's Gravity Referenced Value without Potsdam correction for gravity
data sent to MG&G data base at Lamont.
Further discussion also revealed that 1980 theoretical gravity formula
has incorporated Potsdam correction in its formula.
At the start of the cruise, KSS-30 platform was found turned off. As a result,
there is no data until the start of JD 164.
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
started data processing
|
294
|
1600
|
end of cruise; stopped data processing
|
BGM-3 GRAVITY:
Instrument: Bell Aerospace BGM-3 marine gravity meter
Logging: 1 second intervals
Merge with navigation: calculate Eotvos correction and Free Air
Anomaly.
Checking: Visual check of plot of data to determine satisfactory Eotvos
corrections, reject spikes of data at turns.
Velocity smoothing: 5 point running average throughout the cruise.
Processing:
Since current BGM-3 output has double counts every few minutes the following
scheme has been implemented until the hardware and interface code has been
fixed:
(1) Run a 1 minute Gaussian filter through the data. This will narrow the
output spikes and make them stand out better. Output interval has been
hard-wired to every 15 seconds.
(2) Pass the output through filter1d (see gmtsystem) using -FG480 (an 8 minute
Gaussian filter with robust option, i.e., ignore "outlier" points (i.e. the
spikes).
Calculation:
eotvos_corr = 7.5038 * vel_east * cos(lat) + .004154
* vel*vel
corrected_grv = raw_grv + eotvos_corr - drift - dc_shift
faa = corrected_grv - theoretical_grv
Chief scientist's final data: Observed, Eotvos, Free Air Anomaly value at 00
seconds of each minute.
1980 theoretical gravity formula:
Y0= 978.0327 x ( 1 + .0053024 x sin( [[Theta]]) x sin( [[Theta]]) -
.0000058 x sin( 2 x [[Theta]]) x sin( 2 x [[Theta]]) )
FORMAT: vt.nddd
yy+ddd:hh:mm:ss.mmm N 10 20.1234 W 120 23.1234 1980 77.1
yr. day
time
lat.
lon.
theog FAA
979317.5 64.1 1.5 10.2 -1.7 9.7 -1.6 9.8
raw_grav eotvos drift dc_shift raw_vel smo_vel
Lamont database: Free Air Anomaly value at 00 seconds of each minute.
1930 International gravity formula.
Note:
A '-' sign after the year in the record signifies a flagged record due to turn.
As a result of the discussion among the MG&G group, Lamont Data Reduction
will use Port's Gravity Referenced Value without Potsdam correction for gravity
data sent to MG&G data base at Lamont.
Further discussion also revealed that 1980 theoretical gravity formula
has incorporated Potsdam correction in its formula.
DAY
|
TIME
|
COMMENTS
|
286
|
1530
|
started data processing
|
294
|
1600
|
end of cruise; stopped data processing
|
PRE-CRUISE GRAVITY TIE-IN:
Port: Dutch Harbor, Alaska, U.S.A.
Date: July 6, 1994 (JD 187)
Operator: Bruce A. Francis
Reference Station:
ACIC 2178-1
Reference Value: 981552.07 mGals
Pier/Ship's position:
R/V Ewing was at the pier by the Delta Western Warehouse.
Moved here on July
6th to take on fresh water.
Gravity meter: L & R Model G, serial number 237.
Temperature of meter: 49 oC.
Readings and Calculations:
TIME
|
LOCATION
|
L&R READING
|
G
|
Potsdam Corr?
|
2015Z
|
Pier
|
5046.64+- .05
|
|
|
2032Z
|
Ref
|
5046.43+- .05
|
981552.07
|
NO!
|
2042Z
|
Pier
|
5046.62+- .05
|
|
|
TIME
|
GRAVITY
|
G READING
|
2042Z
|
BGM-3
|
981564.3
|
2042Z
|
KSS-30
|
1396.08
|
Pier reading 2.8 m above waist deck. Waist deck is 5.5 m above gravity meter.
Difference between pier and gravity meter : 5.5 + 2.8 = 8.3 m.
Lacoste difference in LR units:
delta_LR
= pier_LR - ref_LR
0.19
= 5046.62 - 5046.43
Difference in mgal: ( 1 LR unit = 1.06 mGals )
delta_mgal
= delta_LR x constant
0.2
= 0.19 x 1.06
Pier gravity value in mgal: ref_val = G (+13.6 if Potsdam corrected)
pier_grv_val
= ref_val + delta_mgal
981552.27
= 981552.07 + 0.2
Height correction:
Height correction in mGals:
note: free-air constant of +0.31 mGals per meter going towards
the center of earth; -0.31 mGals per meter going away.
hgt_corr
= hgt x constant
2.57 mGals = 8.3 x 0.31 mGals/m
Gravity at gravity meter level in mGals:
grv_at_meter_level = pier_grv_val + hgt_corr
981554.84
= 981552.27 + 2.57
KSS-30:
KSS-30 value was smooth and time adjusted by 75 secs.
KSS_grav_val = kss_unbiased_output + bias
981556.37 = 1396.08 + 980170.29
Mistie in mGals:
mistie = KSS_grv_val - grv_at_meter_level
11.53 = 981556.37 - 981554.84
Drift in mGals since last tie:
prev_mistie: 15.6 mGals on date May 20,1994 (JD 140)
drift = mistie - prev_mistie
-4.07 = 11.53 - 15.6
==> DC Shift = prev_mistie - bias
= 15.6 - 980170.29 = -980154.69
Drift/Day = drift / (tot. # of day)
= -4.07 / (187-140) = -0.0866 mGals/day
BGM-3:
BGM_filt_grv = ( scale factor x counts ) + bias = 979537.0
using s.f. 5.0940744 and bias 8526800, filter width 360. ( 6 minutes)
Mistie in mGals:
mistie = BGM_grv_val - grv_at_meter_level
9.5 = 981564.3 - 981554.84
Drift in mGals since last tie:
prev_mistie: 9.83 mGals on date May 20, 1994 (JD 140)
drift = mistie - prev_mistie
-0.3 = 9.5 - 9.83
==> DC Shift = prev_mistie
= 9.83
Drift/Day = drift / (tot. # of day)
= -0.3 / (187 - 140) = -0.0064 mgals/day
POST-CRUISE GRAVITY TIE-IN:
Port: Balboa, Canal Zone, Panama
Date: 26-27 November, 1994 (JD 330-331)
Operator: Bruce A. Francis
Reference Station:
The site is on the sidewalk on the west of the Captain of the Port building, in
front of main entrance. The station was made in the middle of the circular
concrete section on the sidewalk.
Date: 01 Nov. 1971 Position: N 8o 57.60' W 79o 33.81'
Pier/Ship's position:
R/V Ewing was docked at Pier 16. The tie point is midship, port side.
Gravity meter: L & R Model G, serial number 237.
Temperature of meter: 49 oC.
Readings and Calculations:
TIME
|
LOCATION
|
L&R READING
|
G
|
Potsdam Corr?
|
JD 330 1915Z
|
Pier
|
1919.835+- .05
|
|
|
JD 330 2047Z
|
Ref.
|
1920.810+- .05
|
978224.17
|
YES!!
|
JD 330 2055Z
|
Pier
|
1919.845+- .05
|
|
|
Note: Large tide variation in this port, and at the time of the measurement
above it was difficult to note "C" deck height. It is only good to establish
pier value.
TIME
|
GRAVITY
|
G READING
|
JD 331 1415Z
|
BGM-3
|
978252.06
|
JD 331 1415Z
|
KSS-30
|
1920.99
|
At 1415Z "C" deck was 1.52 m BELOW pier.
"C" deck is 5.5 m above gravity meter.
Difference between pier and gravity lab: 5.5 + 1.52 = 7.02 m
Lacoste difference in LR units:
delta_LR = pier_LR - ref_LR
-1.03 = 1919.84 - 1920.81
Difference in mGals: ( 1 LR unit = 1.0690 mGals )
delta_mgal = delta_LR x constant
-1.1 = -1.03 x 1.0690
Pier gravity value in mGals: rev_val = G + 13.6 if IT IS Potsdam
corrected.
pier_grv_val = ref_val + delta_mgal + 13.6
978236.67 = 978224.17 + (-1.1) + 13.6
Height correction:
Height correction in mGals:
note: free-air constant of +0.31 mGals per meter going towards
the center of earth; -0.31 mGals per meter going away.
hgt_corr = hgt x constant
2.18 mGals = 7.02 x 0.31 mGals/m
Gravity at gravity meter level in mGals:
grv_at_meter_level = pier_grv_val + hgt_corr
978238.85 = 978236.67 + 2.18
KSS-30:
KSS_grav_val = kss_unbiased_output + bias
978249.3 = -1920.99 + 980170.29
Mistie in mGals:
mistie = KSS_grv_val - grv_at_meter_level
10.45 = 978249.3 - 978238.85
Drift in mGals since last tie:
prev_mistie: 11.31 mGals on date Oct. 23, 1994 (JD 296)
drift = mistie - prev_mistie
-0.86 = 10.45 - 11.31
==> DC Shift = prev_mistie - bias
= 11.31 - 980170.29
= -980158.98 mGals
Drift/Day = drift / (tot. # of day)
= -0.86 / (331-296) = -0.02457 mGals/day
BGM-3:
BGM_filt_grv = ( scale factor x counts ) + bias = 979537.0
using s.f. 5.0940744 and bias 8526800.
The count was filtered with a 60 filter width, run thru filter1d -FG480, and
s_bgm
Mistie in mGals:
mistie = BGM_grv_val - grv_at_meter_level
13.21 = 978252.06 - 978238.85
Drift in mGals since last tie:
prev_mistie: 12.02 mGals on date Oct. 23, 1994 (JD 296)
drift = mistie - prev_mistie
1.19 = 13.21 - 12.02
==> DC Shift
Drift/Day
|
= prev_mistie
= 12.02
= drift / (tot. # of day)
= 1.19/ (331-296) = 0.034 mgals/day
|