GPS System Limitations straight from BI Inc, Wisconsins GPS provider

GPS System Limitations

Global Positioning Satellite (GPS) tracking systems were originally designed and utilized by the

military for a variety of purposes, but generally to provide location and/or velocity information

of objects or individuals around the world. GPS has been used in the last decade by civilians to

effectively track vehicles, inventory, Alzheimer’s patients, migrating animals, and even pets.

In community corrections, GPS tracking is a form of intensive supervision used most commonly to

monitor higher-risk individuals under community supervision. Offenders are tracked by a portable

GPS receiver that is carried or worn. In order to provide accurate location information, a receiver

must be in clear sight of at least three satellites. In most normal situations, a human being is likely in

view of between five and eight satellites; however there are basic limitations in GPS technology that

inhibit or block transmissions for brief or extended periods of time.

Known Geographic & Weather Related Limitations

Since satellite transmission power is low, certain geographical conditions may cause problems with

a GPS receiver’s ability to record location data:

Terrain

information if the view of the sky is severely limited. This situation can occur in deep canyons, or

under dense vegetation.

– Signals can become degraded and the receiver system may not provide location

Urban Canyons

fading errors that may affect the ability to track offenders.

– Large or tall buildings grouped closely together can cause large multi-path and

Vehicles

transportation if the receiver is not placed near a window within the vehicle.

– Signals can be lost when an offender is riding in a car or other enclosed means of

Weather

Because of these factors, it is difficult to ensure complete or thorough GPS coverage at all times.

However, with the ongoing advancements in technology, certain system components and features

are now available that improve the equipment capabilities. For example, omni-directional antennas

enable tracking devices to pick up GPS coverage in virtually any orientation. Flat patch antennas are

not as advanced and must maintain an upright position to receive coverage. Reliable radio frequency

(RF) technology, cellular towers and Advanced Forward Link Trilateration (AFLT) can also be paired

with GPS to enhance system accuracy.

Due to the types of individuals normally being supervised with GPS by community corrections

professionals (i.e. higher-risk offenders on parole/probation, pre-trial defendants, etc.), equipment

reliability is imperative. Community safety is a concern if faulty or sub-standard equipment is used

to supervise individuals that may otherwise be in detention, jail or prison. Affordable and effective

alternatives to incarceration are available and agencies must consider the benefits as well as the

system limitations and liabilities that exist with all GPS products.

http://bi.com/sites/all/themes/BI/pdf/GPSlimitations.pdf

Here is a link to BI Inc. GPS page http://bi.com/exacutrackat– Signal strength can become degraded by moisture such as rainfall, fog, or snowfall.