Lab: 1 Image Gathering Fundamentals:  Using a balloon to gather aerial imagery

Introduction:

The purpose of this lab was to explore the fundamentals of aerial image gathering using a balloon and a picavet rig.  This technique is relatively simple, inexpensive method to collect data but requires a substantial amount of time to conduct.  However, this simple lab will help build a foundation of unmanned aerial imaging.  In the following weeks, the class will use more complex methods to obtain and process aerial data.

Study Area:

Photo 1:  Google Maps Satellite photo highlighting the area mapped at the Eau Claire Soccer Park.  

The Eau Claire Soccer Park is located two miles South of the University of Wisconsin- Eau Claire Campus on the corner of West Hamilton Ave. and Craig Road. This location was ideal for balloon photography because of the available open space and flat topography.  Furthermore, wind speeds were a minimum at ground level, which made it easy to keep the balloon flying relatively straight lines.  

Methods:

Setting up the balloon/picavet rig is the most important step in the lab because it controls what quality of data will be obtained. To set up the lab, the balloon is first filled with enough helium to carry two SX260 cameras at an altitude of 150ft (Photo 2).  After securing the balloon to the picavet rig, the balloon end is sealed with multiple zip-ties so that helium does not escape mid-flight (Photo 3).  Lastly, the cameras, one of which modified for near infrared, is secured on a picavet rig (Photo 4) 15ft below the balloon to capture images at a near vertical angle (nadir).  After the balloon is attached to the string and released into the air, an individual must walk in straight lines with the balloon up and down the field, spaced at 30ft intervals to ensure proper overlap of the images.  An overlap ranging between 75-85% was obtained during this lab to ensure that the pictures could be properly stitched together during the data processing.

   Photo 2: Filling the balloon with helium

Photo 3:  Sealing the end of the balloon and attaching it to the picavet rig.

Photo 4: Attaching the cameras

Discussion:

The data obtained from this lab has not yet been processed so the results are not yet known.  After the data is processed, we will have a better understanding of what should be done in the future to obtain a higher quality data set.  The cameras used in the lab were programmed to take picture every five seconds based on the speed the balloon is able to move.  However, because this was a group experiment, it is recognized that some individuals likely walked quicker than others.  Although it is doubtful that any student walked quick enough to prevent sufficient front and back overlap, students walking at slower speeds may cause too much of an overlap in certain areas.  Although this increases the quality of the data, it can also increase the process time of the data dramatically.  Overall, it is important to set the frame rate of the camera according to the the speed the aircraft/device, and based on the quality of the data required for the project.

From this lab, I also learned that independent variables such as wind speed, sunlight, and atmospheric conditions must be considered.  Fortunately for this activity, wind speeds were low, allowing the rig to move without swaying substantially from side to side.  However, path obstacles such as benches, trees, and other structures may have caused the balloon to sway as the individual moved around them.

Conclusion:

As a Geology major, I do not have an advanced level of knowledge on spatial systems like other members of the class.  Even though I walked into the lab knowing very little, I came out of the lab knowing the different aspects of basic image gathering.  This method is relatively low tech, and is effective for small, cleared, areas where obstacles are not a significant factor.  For application to large scale mining (my focus for this course), more advanced methods of mapping are required because the areas cannot be mapped on foot.  I am excited to dive into these more advanced methods, and begin learning the different methods of data analysis.