Puerto Rico Airborne Gravity Data Modeling

Kevin Brodie IINorfolk State University, Virginia

Computer Science

Dr. Theresa Damiani (Mentor)National Geodetic Survey

Resilient Coastal Communities and Economies

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Overview

• What is Geodesy?

• Background

• Puerto Rico

• Hypothesis

• Methodology

• Results

• Discussion/Future Work

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Geodesy is…

• The science of measuring the size and shape of the earth, including the gravitational field and its locations throughout different points in an area.

Geoid is simply a surface of equal gravity potential energy. The Earth’s mass is unequally distributed causing certain areas to have a greater gravitational pull which makes the geoid seem to have bulges.

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Background• The Airborne gravity data was collected by the

National Geodetic Survey’s GRAV-D program there in 2009. GRAV-D surveyed Puerto Rico and the islands in the marine areas to the north and south, where the Puerto Rico trench and other ocean floor features are located.

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Caribbean

Atlantic

About Puerto RicoDifferent classification schemes exist for the soils of Puerto Rico. 

Five general soil types: humid coastal plains, semiarid coastal plains, humid uplands, semiarid uplands, and humid upland valleys. 

The territory is very mountainous (covering about 60%), except in the regional coasts, but Puerto Rico offers astonishing variety: rain forest, deserts, beaches, caves, oceans and rivers.

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HypothesisThis research project has the objective of better understanding the setting and geologic composition of PRVI, which is important for NOAA’s use in geodetic modeling of the area.

We hypothesize that using gravity data files for the 2D modeling of topography and bathymetry of PRVI, gravity anomalies, that are produced from algorithms of code, can be calculated and graphed in MATLAB. Finally the created 2D model will have polygons that are added that mimic oceanic crust and mantle. These polygons drastically effect the model’s gravity and are tweaked in order for the model gravity to match actual airborne gravity survey data in 2009. Then the model that is created is interpreted in order to better understand the composition of the islands.

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Methodology

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Latitude Longitude Full-field gravity (mGal)

Free-air gravity(mGal)

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Topography

Caribbean Bathymetry

Atlantic Bathymetry

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For each polygon there is a calculation done for each point separately to find the gravity.

A rigorous process of editing the model to produce a similar gravity reading to the measured gravity is done.

Oceanic Crust density=2.9733

Mantle density=3.3

This boundary that separates two different densities of rock is what gives the gravity reading

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Mantle density =3.3 g/cm

Oceanic Crust Density = 2.97 g/cm

Results This project was the 1st step in

modeling more complex diagrams and figures of the PRVI

The topographic and bathymetric models of PRVI were created with MATLAB; along with that, realistic gravity signals were calculated using different algorithms.

Gravity and model results were consistent among other researchers work.

There was a distinct protruding mass of mantle that was found and observed.

Knowing the gravity, sea level can be located, which in turn improves the accuracy of elevation measurements in Puerto Rico

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Caribbean plate

Atlantic plate

Discussion/Future Work

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Knowing where the density changes among land, gravity can be calculated

Based off of the gravity information, Sea level can be located

With actual Sea level heights known, the vertical datum can be updated

With the vertical datum more accurate, this allows the coastal communities to be further prepared for natural disasters

This project was one component of many that leads to the updating of the vertical datum.

Resilient Coastal Communities and Economies

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Images collected by NGS emergency response team of post-Sandy destruction. Houses and roads washed away by storm surge illustrate the importance of knowing sea level and heights above sea level. Coastal communities can rebound from storms more quickly, with less damage, if we know which areas are in the most danger from rising waters during storms

Acknowledgements

• A special thank you to:

- Dr. Theresa Damiani- National Geodetic Survey- Office of Education Scholarship Team

- Fellow EPP Scholars

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