Design to Improve the Productivity and
Execution of Gravity Surveys
Evan Demick
Kyle Luukkonen
Sadeep Nonis
Yuri Zhylenko
Sponsor: Sandra Preaux - NOAA
Agenda
 Context Review
 Stakeholder Analysis
 Problem & Need Statements
 Method of Analysis & Simulation
 Recommendation & Conclusion
2
What is a Gravity Survey?
 Collection of measurements of the acceleration of
gravity.
 Accelerations are used to model the earth’s geoid.
 The geoid model is used
to determine elevations.
 Mountains have greater mass
than a valley, so the pull of
gravity is stronger near
mountains
http://celebrating200years.noaa.gov/foundations/gravity_surveys/welcome.html
3
Importance of Gravity Surveys
 Accurately measure the height and flow of water in
flat areas to make efficient use of water resources.
 Variations in gravity represent different densities
beneath the surface.
 Variations may represent petroleum, natural gas, and
various metals.
 Plan evacuation routes for low lying coastal areas.
 FEMA requires the use of survey data for flood control
certificates.
http://www.ngs.noaa.gov/PUBS_LIB/SocioEconomicBenefitsofCORSandGRAV-D.pdf
4
History of Gravity Surveys
 National Geodetic Vertical Datum of 1929 (NGVD 29)
 Originally known as the Sea Level Datum of 1929.
 Based on mean sea level (MSL) at 26 tidal gauges
between the United States and Canada.

21 in the U.S. and 5 in Canada
 Defined by the observed heights at each tidal gauge and
the elevations of all benchmark locations.
 MSL is not a constant.

Impacted through wind, atmospheric pressure, water
temperature and salinity.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
5
History of Gravity Surveys
 North American Vertical
Datum of 1988
 NAVD ‘88 was established




in 1991 to replace NGVD
29’.
Data points collected
through geodetic leveling
and satellites.
Data is very sparse.
Errors in measurements as
high as 2 meters.
Majority of data collected
in the 70’s and 80’s.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
6
Gravity for the Redefinition of the
American Vertical Datum (GRAV-D)
 Created in 2007 to complete a thorough survey of the
gravity field over the United States and it’s territories.
 NGS Federally Mandated project (80-373).
 Designed to replace existing gravity measurements
from NAVD ‘88.
 Could see a potential economic benefit of $4.8 billion
over fifteen years.
 Based primarily on flood plain mapping and avoidance
costs for leveling.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
7
Logistics Diagram
8
Annual Target Identification
FY13
FY14 FY15 FY16 FY17 FY18 FY19 FY20 FY21 FY22
28%
36%
44%
52%
60%
68%
76%
84%
92% 100%
 Percentages represent the annual goals for the GRAV-
D project starting in FY2013.
 Currently, NOAA has been reaching their yearly
targets of 5.6% per year.
 NOAA will need to increase yearly output to 8% to
reach 2022 completion goal.
9
Project Gap
120
23%
Percentage Complete
100
80
Target
60
Actual
Projected
40
20
0
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Years
Targeted Completion Year - 2022
10
Historical Survey Data
 Timeframe – 2008 through 2012
 Important factors
 Weather, Aircraft Maintenance, Aircraft Repair,
Instrument Issues, and Personnel Days.
11
Survey Zones
12
Historical Data Distributions
Factors
Type of
Distribution
Mean
(days)
Standard Deviation
(days)
Square Error
Aircraft
Maintenance
Beta
5.57
8.18
0.036
Aircraft Repair
Beta
3.85
6.77
0.025
Equipment
Repair
Beta
2.14
3.80
0.035
Weather Delay
Beta
4.98
4.00
0.021
Personnel Day
Gamma
3.06
1.84
0.005
13
Deming’s Theory
Theory - Anomalies in quality are variations outside the
control limits of a process.
W. Edwards Deming
 To meet program target completion goals the variation
of the delays in each process must be reduced.
Quality
Variance
14
Agenda
 Context Review
 Stakeholder Analysis
 Problem & Need Statements
 Method of Analysis & Simulation
 Recommendation & Conclusion
15
Stakeholder Relationship Diagram
16
Planning Stakeholders
Stakeholders
Objectives
Tensions
NOAA
Responsible for project
management.
Limited funding for
implementing gravitational
survey.
Airplane Contractors
Supports gravitational
survey objectives.
Limitations on flight paths
and aircraft use.
Pilots and Support
Crews
Main objective is to collect
physical data.
Limited amount of time
and funding.
Department of
Commerce
Provides funding for
project.
Requires annual
completion targets.
Residents
Receive elevation
measurements.
Needs to give additional
support to NOAA
FEMA
Acquire the survey data for
flood control certificates.
Limited on survey data
completed for flood control
certificates.
17
Stakeholder Relationship Diagram
18
Execution Stakeholders
Stakeholders
Objectives
Tensions
NOAA
Responsible for project
management.
Limited funding for
implementing gravitational
survey.
Pilots
Flies the planes to allow the
data to be collected.
Limited hours that can be
flown.
Ground Crews
Repairs the planes.
Limited amount of time
and supplies or parts for
repairs.
Surveyors
Collects the physical datum.
Limited amount of time
and accuracy with
equipment.
19
Agenda
 Context Review
 Stakeholder Analysis
 Problem & Need Statements
 Method of Analysis & Simulation
 Recommendation & Conclusion
20
Problem Statement
 NOAA has to reach 8% geographic area coverage
annually.
 A plan to reduce variability within the
gravitational survey is needed to maximize
coverage within budget.
 Before Fiscal Year 2022
21
Need Statement
 NOAA must complete the 8% annual quota but receives limited
funding from the Department of Commerce.
 Making the gravity survey reduce variability will remove the
tension with the Department of Commerce on NOAA’s need for
more financial backing by decreasing the time needed to
complete a survey block.
22
Agenda
 Context Review
 Stakeholder Analysis
 Problem & Need Statements
 Method of Analysis & Simulation
 Recommendation & Conclusion
23
Design Alternatives
 Alternative 1
 Focus on Logistics Process

Improve the execution of gravitational surveys and reduce
variance in several variables which cause extra delays and
unnecessary downtime.
 Alternative 2
 Acquire additional resources

The number of aircraft, equipment suites, and personnel
limits the amount of surveys that can be completed annually.
 Alternative 3
 Combine Alternatives 1 & 2

Maximizes the output, but is constrained by budget.
24
Value Hierarchy
US Gravity Survey
Area Coverage
Availability
Time
(0.43)
(0.35)
(0.22)
25
Black Box Model
Simulation
 Used historical data to build a distribution for each
process block.
 Assume process independence.
 Run the simulation for 10,000 replications and
compare results.
Verification – Data Comparison
 Simulation Output (Base Case)
 Mean: 44.01 days
 Worst case: 110.45 days
 Historical Data Analysis
 Mean: 41.63 days
 Worst Survey: 76 days
 Worst Values: 130 days
Verification – Data Correlation
Weather Delay
Aircraft
Maintenance
Aircraft Repair
Equipment
Repair
Personnel Day
Weather Delay
Aircraft
Maintenance
Aircraft Repair
Equipment
Repair
Personnel Day
1
-0.21
-0.066
0.49
0.17
1
-0.0055
-0.16
0.62
1
-0.029
-0.24
1
0.33
1
 Symmetric correlation coefficient
 Negative relationship – As the duration of one process increases,
the duration of the corresponding process decreases
 Positive relationship – As the duration of one process increases,
the duration of the corresponding process increases
29
Design of Experiment
 Reduce the variance of each input variable by 5%, 10%,
15%, 20%, and 25%.
 Run 10,000 replications after each change.
 Calculate the days to completion.
 (10%) = (μ - min) * 0.2 + min
 (50%) = μ
 (90%) = (max - μ) * 0.8 + μ
 Analyze which variables have the biggest impact on
the survey by subtracting the new value from the base
case.
Data Analysis
Inputs
Outputs
Process
Variance Reduction 10% to completion (days) 50% to completion (days) 90% to completion (days)
5%
22.67
43.97
96.79
10%
22.66
43.92
96.38
Aircraft
15%
22.64
43.82
95.80
Maintenance
20%
22.92
43.44
92.88
25%
22.98
43.38
92.46
5%
22.66
43.94
96.95
10%
22.65
43.88
96.71
15%
Aircraft Repair
22.64
43.84
96.46
20%
22.63
43.80
96.19
25%
22.62
43.74
95.87
5%
22.71
43.99
96.94
10%
22.74
43.96
96.70
15%
Equipment Repair
22.77
43.93
96.47
20%
22.79
43.87
96.16
25%
22.97
43.74
94.15
5%
22.67
44.01
97.20
10%
22.67
44.00
97.24
15%
Weather Delay
22.67
44.01
97.27
20%
22.67
44.00
97.30
25%
22.67
43.97
97.31
5%
23.16
44.01
96.71
10%
23.11
44.01
96.66
15%
Personnel Day
23.07
44.01
96.61
20%
23.04
44.01
96.57
Results
Variance Reduction vs Base Case (90% to completion)
5
Time Saved (days)
4
3
Aircraft Maintenace
Aircraft Repair
2
Equipment Repair
Weather Delay
1
Personnel Day
0
5%
-1
10%
15%
20%
Variance Reduction (%)
25%
Results
Factors
Rank in
Variability
Max Delay
Reduction
(days)
Mitigation Strategies
Aircraft
Maintenance
1
4.70
Additional maintenance personnel.
Preventative maintenance.
Aircraft Repair
3
1.29
Improved maintenance.
Available spare parts.
Equipment
Repair
2
3.01
Back up equipment.
Weather Delay
5
-0.15
Weather analysis from regional
historical data.
Personnel Day
4
0.63
Schedule days off around other delays.
33
Utility
Utility vs Cost
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2500000 2700000 2900000 3100000 3300000 3500000
Cost ($)
34
Agenda
 Context Review
 Stakeholder Analysis
 Problem & Need Statements
 Method of Analysis & Simulation
 Recommendation & Conclusion
35
Recommendations
 Alternative 1 – Focus on the logistics process of the
surveys by allocating budget and resources towards
improving parameters based on their rank in
variability.
 This method has the least cost while still providing good
way for survey execution based on the output value.
 Follow delay mitigation strategies to maximize the
performance and data gathering of the survey.
36
Conclusion
 Variability reduction will reduce the time to conduct
an average survey by 3 - 9 days based on 25%
variability reduction.
 More surveys will be completed in 44 days or less.
 Save up to 47.4 days of survey time annually.
 Enough time to conduct another survey.
 Fewer days spent on survey results in less spending.
37
38
EXTRA SLIDES/OLD SLIDES
39
Design to Improve the Productivity and
Execution of Gravity Surveys
Evan Demick, Kyle Luukkonen,
Sadeep Nonis, Yuri Zhylenko
40
National Geodetic Survey
 The National Geodetic Survey (NGS) has a clearly defined
mission statement:
 “Define, maintain and provide access to the National Spatial
Reference System (NSRS) to meet our nation’s economic,
social, and environmental needs.” (NOAA 2012)
 The National Geodetic Survey (NGS) is a government
supported program that provides positioning information
to the nation.
 NGS has several different projects currently underway
(including GRAV-D and CORS) to aid in the measuring of
elevation, longitude, latitude, and shoreline data.
41
History of Gravity Surveys
 NAVD ‘88 was established in 1991 to replace the
existing Sea Level Datum from 1929.
 Surface measurements were taken using a technique
called leveling.
◦ Surveys were conducted over many
years by numerous outside sources.
Data is very sparse.
◦ Locations like Alaska have very few
measurements due to terrain.
◦ A gap is also present along the
coastlines.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
42
North American Vertical Datum
 Measurements are outdated and have been skewed
due to crustal movements (last collected in the 70’s
and 80’s).
 Many markings have been destroyed by regional
development and poor maintenance.
 There is a transcontinental tilt from the SE to NW of
the U.S. for short wavelength gravity measurements.
 Errors in measurements as high as 2 meters.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
43
Importance of Gravity Surveys
 FEMA requires the use of survey data for flood control
certificates.
 Floodplain maps also determine whether or not homes
or buildings require flood insurance under the National
Flood Insurance Program

A FEMA run program with over $650 billion in insured assets.
 Mapping gravity can improve the accuracy of atomic
clocks which are used in many electronic systems.
 Provide measurements that are geographically
continuous rather than points based on physical
monuments.
http://www.ngs.noaa.gov/PUBS_LIB/SocioEconomicBenefitsofCORSandGRAV-D.pdf
44
Importance of Gravity Surveys
Floodplain maps are used to determine land use and building
code requirements.
Builders must have site plans and matching elevation data to
help minimize any potential damage.
Planning the development of new buildings and infrastructure.
Variations in gravity represent different densities beneath the
surface which can be used to detect petroleum, natural gas,
and various metals.
 Mapping gravity can improve the accuracy of atomic clocks
which are used in many electronic systems.
 Provide measurements that are geographically continuous
rather than points based on physical monuments.
45
Importance of Gravity Surveys
 Road construction currently uses conventional
geodetic leveling.
 Upgraded gravity surveys could replace conventional
leveling for road works and save state and local
municipalities as much as $300 billion per year.
 Replace leveling for sewage systems, water supply, and
mass transit activities.
 Monitor changes over time in crustal motion to predict
earthquakes and water flow.
http://www.ngs.noaa.gov/PUBS_LIB/SocioEconomicBenefitsofCORSandGRAV-D.pdf
46
GRAV-D Objectives
 Redefine the US vertical datum and replace geodetic
leveling in large areas with GPS measurements and a
gravimetric geoid model to determine orthometric
heights.
 Redefine and improve the vertical component of
NSRS.
 Provide a vertical datum that is more economical than
traditional leveling.
http://www.ngs.noaa.gov/PUBS_LIB/SocioEconomicBenefitsofCORSandGRAV-D.pdf
47
Equipment
 A test mass is first dropped and allowed to fall freely inside a





vacuum chamber.
The test mass will fall roughly 7 cm and the actual distance will
be measured precisely using a laser interferometer and a
rubidium standard atomic clock.
As the test body falls, optical interference fringes are generated
by the laser interferometer.
These fringes are counted and timed with the atomic clock.
The measurements of time and distance are then fitted to a
parabolic trajectory that produces an accurate measure of the
gravitational acceleration.
The A10 provides measurements without the need for postprocessing, and so reduces any additional overhead required to
run the machine.
48
Areas with Completed Surveys
 The GRAV-D program has already covered several
areas since starting in 2007.
 Eastern Alaska.
 Gulf of Mexico (focusing primarily on Louisiana and
areas struck by Hurricane Katrina).
 The Great Lakes Region.
 California Coastline.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
49
Survey Area Layout
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
50
Survey Area Layout Design
Google Earth Image Provided by NOAA - 2012
51
Areas with Completed Surveys
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
52
Types of Wavelength Measurements
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
53
Process for Completing Survey
54
 Measurements closeMeasurements
to the planet capture shortWavelength
wavelength and low-magnitude features.
 Measurements by plane capture intermediatewavelength and midrange-magnitude features.
 Measurements by the satellites “GOCE” and “GRACE”
capture long-wavelength and high-magnitude
features.
 The satellites measure in 250x250 km data points and
because of this the Satellite data cannot help fix the
surface data because many of the surface surveys are
smaller than 200x200 km.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
55
GRAV – D
 Ellipsoidal heights are more common and much easier
to find using GPS technology.
 Cannot be used to model water flow.
 Orthometric heights are related to water flow and can
be used in floodplain mapping.
 Sometimes referred to as “height above sea level”
 To find orthometric heights, a model of the geoid must
be created using measurements of the acceleration of
gravity near the earth’s surface.
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
56
Coast and Geodetic Survey Act
 Public Law 80-373
 Objective is to provide a national coordinated spatial
reference system.
 Will provide orientation, coordinated positions, and
elevations at specific points for mapping, planning, and
development.
 Extend the National Spatial Reference System into areas
that are not currently covered to meet infrastructure
needs.
https://www.cfda.gov/?s=program&mode=form&tab=step1&id=40dbf9b68027de96a134c38f069efa3d
57
Equipment
 The main pieces of technology in an equipment
suite are a Gravimeter, Inertial Measurement
Unit (IMU), and GPS Base station
 A gravimeter is a device used to measure the
vertical acceleration of gravity on the earth’s
surface.
 The gravimeters run on the Turnkey Airborne
Gravity System (TAGS).
 An IMU utilizes three accelerometers and three
gyroscopes to measure the aircrafts current
rotation and acceleration.
 A base station is a GPS receiver at a fixed
location.
 It gives corrected position data for increased
accuracy.
58
Project Constraints
 NGS only owns two equipment suites, so only two field




teams may run at one time
$2.4 million budget per year for all survey operations
(including aircraft, fuel, pilots, and NOAA personnel
travel costs)
Must use an airport with contract fuel when working
on a government aircraft
A standard block is 400 km by 500 km, which is
approximately a 100 flight hour survey
Blocks must overlap by 30 - 40 km on the sides to
make the survey data continuous
59
Project Constraints
 Generally northern areas in the summer, southern




areas in the winter
Avoid Eastern seaboard (especially SE) during
Hurricane season
Avoid Tornado Alley in Spring and Fall
Go to Oregon/Washington area June-August
Go to Western Alaska June - September
60
Contract Aircraft Availability
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
61
Constraints
62
Distribution for Survey Days
63
Distribution for Weather
64
Project Constraints
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
65
Project Constraints
http://geodesy.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf
66
Process Controllable
Chart
Process
Tensions (affects air crews, contractors, and
NOAA’s projected time for completion)
Transit
no
Time variability affects total completion time
for survey
Prep
no
Time variability affects total completion time
for survey
Survey
yes
Data collection time restraints and accuracy
of measurements
Break-down Delays
yes
Unplanned time delay
Weather Delays
no
Unplanned time delay, seasonal awareness
can aid delay severity
Equipment
Removal
no
Low time variability calls for no variability
reduction analysis
67
Planning Procedure
 Map out the survey blocks across all the required
regions
 Select airports that maximize area coverage and meet
the necessary constraints
 Assign survey blocks to each aircraft for a specific year
 Calculate the total cost by adding all the variables
 Fuel cost, hangar cost, hourly wages, hotel / meal cost,
travel cost
 Calculate cost risk for design comparison
68
Need Statement (old)
 NOAA needs to complete the 8% annual quota but receives limited
funding from the Department of Commerce.
 Making the gravity survey more efficient will remove the tension with the
Department of Commerce on NOAA’s need for more budget.
 Each Airplane Contractor needs to have their planes used evenly and
fairly.
 The plan that is created needs to not rule out certain aircraft based on its
constraints to minimize tension between each Airplane Contractor.
 NOAA needs the physical gravity datum but the pilots and support
crews have a limited amount of time that they can work.
 NOAA needs to hire more pilots and/or implement a more efficient use of
the pilot’s hours to maximize time in the air for gravity surveys.
 NOAA tries to prioritize each state based on State Government
requests.
 NOAA needs to be willing to deviate from their set flight plans if in return
a State Government can help fund the gravity survey.
69
Problem Statement (old)
 NOAA needs to complete 8% coverage of Continental
U.S., Alaska, Hawaii, Puerto Rico, U.S. Virgin Islands,
Guam, and American Samoa per year. Since 2008
NOAA has not reached their annual goal and have only
covered around 5-6% per year of the U.S. and
territories. A plan to reduce variability within NOAA's
budget is needed to reach their 8% per year quota so
they can complete the GRAV-D project by the Fiscal
Year 2022.
70
Survey Data
71
Survey Data
72
Survey Data
73
Cost Estimation
74
Sample Cost Calculation
Total Cost = (Total Fuel Cost + Total Per Diem Cost) × 110%
(The addition of 10% simulates additional known—but difficult to
pre-estimate—costs, such as shipping, etc.).
75
Distribution for Prep
76
Distribution for Transit
77
Distribution for Aircraft Maintenance
78
Distribution for Instrument Issues
79
Distribution for Personnel Day
80
Design Alternatives
 Allocate current resources which would reduce the
variance in major points of the project.
 Currently, NOAA operates with six aircraft, 4 teams, and
two equipment packages.
 Determine major factors in reducing variability (backup
aircraft or equipment maintenance).
 Add additional resources.
 To reduce variability add additional aircraft, equipment
suites, or personnel.
81
Design Alternatives
 Allocate current resources (focus on performance).
 Currently, NOAA operates with six aircraft, 4 teams, and
two equipment suites.
 Determine major factors in reducing variability (backup
aircraft or equipment maintenance).
 Add additional resources (focus on availability).
 To reduce variability add additional aircraft, equipment
suites, or personnel.
 Add additional contract aircraft to increase aircraft
availability.
 Additional resources and allocation (combination)
82
Design Alternatives
 The second alternative would be to add additional
resources such as aircraft, equipment suites, or
personnel as well as allocating them in an optimal
manner.
 By having limited resources, NOAA is severely deterred
in the number of surveys they can complete during a
fiscal year. Additional assets will cost more money, but
will speed up the process by allowing multiple surveys to
be done at the same time and may be more beneficial in
the long run of the project.
83
Sensitivity Analysis
 Identify Parameter with biggest impact on time and
cost.
 Identify the percent change in a parameter to…
84
Preliminary Recommendations
 Our simulation is similar to the real thing
85
Base Case
Aircraft Maintenance -5%
Aircraft Maintenance -10%
Aircraft Maintenance -15%
Aircraft Maintenance -20%
Aircraft Maintenance -25%
Aircraft Repair -5%
Aircraft Repair -10%
Aircraft Repair -15%
Aircraft Repair -20%
Aircraft Repair -25%
Equipment Repair -5%
Equipment Repair -10%
Equipment Repair -15%
Equipment Repair -20%
Equipment Repair -25%
Weather Delay -5%
Weather Delay -10%
Weather Delay -15%
Weather Delay -20%
Weather Delay -25%
Personnel Day -5%
Personnel Day -10%
Personnel Day -15%
Personnel Day -20%
Personnel Day -25%
Base Case vs Variance Reduction
Reduction vs Base Case (10% to completion)
0.1
0
5%
10%
15%
20%
25%
Time Saved (days)
-0.1
Aircraft Maintenace
-0.2
Aircraft Repair
Equipment Repair
-0.3
Weather Delay
Personnel Day
-0.4
-0.5
-0.6
Variance Reduction (%)
Base Case vs Variance Reduction
Reduction vs Base Case (50% to completion)
0.7
0.6
Time Saved (days)
0.5
0.4
Aircraft Maintenace
Aircraft Repair
Equipment Repair
0.3
Weather Delay
Personnel Day
0.2
0.1
0
5%
10%
15%
Variance Reduction (%)
20%
25%
Works Cited
 GRAV-D Science Team (2011). "Gravity for the Redefinition of the American Vertical





Datum (GRAV-D) Project, Airborne Gravity Data; Block AS01". Available
09/28/2012. Online at: http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml
GRAV-D Science Team (2011). "Block AS01 (Central South 01); GRAV-D Airborne
Gravity Data User Manual." Theresa Diehl, ed. Version 1. Available 09/28/2012.
Online at: http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml
GRAV-D Science Team (2011). "GRAV-D General Airborne Gravity Data User
Manual." Theresa Diehl, ed. Version 1. Available 09/28/2012. Online at:
http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml
LaCoste , Micro-g . "A-10 Gravimeter User’s Manual." A-10 Outdoor Absolute
Gravimeter. Micro-g LaCoste, July 2008. Web. 10 Oct 2012.
<http://www.microglacoste.com/pdf/A-10Manual.pdf>.
"IEEE-USA Consultants Fee Survey Report." Exality.com. IEEE-USA E-Books, 2011.
Web. 14 Oct. 2012. <http://www.exality.com/files/ConsultantFeeSurvey2011.pdf>.
Special thanks to the project managers at NOAA for providing much of the
information needed for the context and constraints.
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