Optical Aurora Detector

Students: Steve Gates, Nicole Lerner

Sponsor: NASA Space Grant Consortium

Faculty Advisor: Dr. Joseph Shaw

Fall Semester 2009

An aurora over the Bridger range. Photo courtesy of Dr. Joseph Shaw.

Project Description and Design Goals:

The underlying objective of this project is to improve upon a preexisting device that detects the presence of auroras in the night sky. Past design teams have designed, constructed and tested a working model of the aurora detector. In brief, the detector functions by monitoring the night sky for light with a 557.7 nm wavelength (the green color characteristic of auroras). Complementary to this green light detector, a white light detector is currently used to supply an on/off signal to the green light detector by detecting the general darkness of night (this signal turns off the green light detector during the daylight hours). In its current state the aurora detector is reporting a high level of false positives. Examining the data shows numerous, unexplained peaks at 557.7 nm which are causing the false positives. The goal of this project is to drastically decrease the percentage of false positives reported by the aurora detector.

To decrease the detector�s false positives, two complementary approaches will be carried out. First, the green light detector will be optimized to filter out any stray light that may be causing the false positives. This optimization will involve characterizing and purposefully setting the field of view of the green light detector, as well mechanical modifications to the optical setup. The second approach to decreasing false positives will focus on moving the white light detector�s functionality beyond simply signaling when �night� has arrived. Currently the white light detector lacks the dynamic range to resolve brightness at the levels the false positives occur. To increase the dynamic range of the white light detector its photodiode will be reevaluated and its gain optimized to provide useful information at the desired brightness levels. The intent is to optimize the white light detector to the point that its data can be used as a complementary signal in the detection algorithm.

The practical purpose of this project is to aid in the understanding and observation of auroras. The end goal (on a timeframe beyond the range of this semester�s work) is to have the detector send a text message to a list of subscribers whenever an aurora is visible in the night sky. In this way the device will make aurora observation more accessible and will facilitate learning and understanding.

Engineering Constraints:

Throughout the design process, many factors beyond the technical aspects of the design are being considered including: economic, environmental, sustainability, manufacturability, and health and safety constraints. These design impacts were deemed of significant importance due to the possibility that each one can affect the overall quality and functionality of the final product.

Economic:

As is the case with any project it is preferable to produce the best possible outcome at the lowest possible cost. This is especially true of the future kit based aurora detector.
Economic factors include the initial cost of each component going into the kit, the working lifetime of each component, and the assembly time for the kit.

Environmental:

The detector should not disrupt the viewing experience of a human aurora observer. The detector should therefore not emit light or noise pollution.
The detector should not affect or be affected by wildlife.
The detector's materials should not corrode or harm the environment.

Sustainability:

In order to operate autonomously for long periods of time the detector will need to be robust enough to function and withstand all reasonable types of weather.

Manufacturability:

The detector should be designed with human kit assembly in mind. For example the smallest, most compact design is not desirable since the cramped spaces would make assembly and maintenance difficult.
Most of the components will be off the shelf parts, however the external casing will most likely need to be custom ordered or standard ordered and modified. This decision will depend mainly on the cost of each option and the quantity expected to be produced.

Health and Safety:

Kit assembly introduces the risk of injury during the assembly process. The most probable injury is electric shock, especially since the green light photomultiplier tube (PMT) uses hundreds of volts. However, the PMT component is a self contained module that only requires 13.5 V at its input. By including a detailed assembly manual the risk of injury during the assembly process should be minimal.
Placing the detector in its observation location may pose a safety risk in the sense that the location may be high off the ground to reduce ground scattered light. To lessen the safety risk the detector casing will be designed with mounting brackets that make installation straightforward and quick.

The previously designed detector. The green channel PMT looks out the window on the right, the white channel photodiode is on the left looking the same direction. Photo courtesy of Dr. Joseph Shaw.