gravityapp

Depending on where you are on Earth, the acceleration due to gravity differs from the SI constant of 9.80665 m/s2. These fluctuations in gravity are due to both the geology and altitude at that location.

NASA's GRACE and GOCE missions use satellites to provide a precise description of Earth's geoid, which provides insight into the gravitational force at a given location. The data from these missions is made available in several different forms.

Our team was able to use this data to build an API that would provide, for a given a latitude and longitude, the force of gravity for that location. On top of this API, we designed and built an iPhone app that uses the phone's location data to query for and display this information.

The API uses data from the Western Australian Center for Geodesy (http://geodesy.curtin.edu.au/research/models/GGMplus/), which we've hosted on Amazon S3. When a location is sent to the API, it calculates the correct file and byte location in > 80 GB of data and returns the gravity acceleration at that point.

Currently, this data is a composite gravity field model that is derived from several different sources (such as GRACE, EGM 2008, etc.), so the data is not realtime. In the future, we'd like to be able to use both this data as well as theoretical data calculated by the spherical geopotential approximation to provide measurements that are more accurate.

Since gravity field models for the moon and Mars exist as well, another future improvement would be to include this data in the app and let the user compare the various gravity fields.

We hope that this app will serve as an educational resource for those that may not know that gravity fluctuates throughout the planet.

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