Aerial Mapping Using Near-Infrared Imaging: The Bioswale at Carpenter's Orchard

Introduction:

• What did you set out to do, and why? What is the question?
  • Our group set out to photograph with the near-infrared feature on our camera the bioswale in Carpenter's Orchard on the Thacher campus in order to create a map. The near-infrared camera can help us gauge the health of the vegetation through showing levels of photosynthetic activity and thus give us a sense the effectiveness of the bioswale in channeling and mitigating nutrient pollution.
    • "NDVI stands for "Normalized Difference Vegetation Index". NRG stands for "Near-infrared / Red / Green". NDVI and NRG are both ways to visualize the amounts of infrared and other wavelengths of light reflected from vegetation. Because both these methods compare ratios of blue and red light absorbed versus green and IR light reflected, they can be used to evaluate the health of vegetation. It's a snapshot of how much photosynthesis is happening. This is helpful in assessing vegetative health or stress." - Infragram, Public Lab
• What did you already know about the question/problem?
  • A bioswale is an earthen berm whose function is to channel nutrients and polluted water into a specific area to be taken up by plants, thus purifying the water and reducing nutrient pollution from Carpenter's Orchard from entering the nearby Eastern Tributaries of Thacher Creek that drain Thacher Canyon and Carpenter's Orchard.
  • It was constructed by Justin Miles and Anna Fleming in 2013 as part of their Kumana project.
  • From our ground observations, we believe the bioswale is somewhat effective due to the presence of numerous species of plants within the fence. One of the uses of our aerial map is to confirm or deny the effectiveness bioswale in channeling nutrient polluted water from Carpenter's Orchard into the bioswale and allowing plants to use those nutrients.
• Why is aerial mapping a good way to make a contribution to this problem?
  • Using aerial mapping with a near-infrared camera, one can discern the health of vegetation surrounding Carpenter's Orchard and where pasture runoff is being channelled by looking at our aerial images for evidence of ruts caused by runoff and the contours of the land that would naturally channel runoff into the bioswale. With this information we can assess how successful the bioswale is at channeling nutrient rich water into an area where it can used by plants instead of flowing into local creeks and causing nutrient pollution and possible eutrophication.

Methods:

• Equipment
  • We used a 5.5 foot Cloudbuster helium balloon with a long string to get the camera, a Canon PowerShot A2200 (14.1 megapixels), high enough to take the photos we needed. We used the near-infrared feature on the camera which was modified by using a filter from the Public Lab NIR kit and inserting it in front of the camera's sensor. To harness the camera to the balloon, we used a carriage constructed from the top of a recycled plastic juice container with a fin made from hard plastic strips to stabilize the carriage in flight. To harness to camera to the carriage, we made a sling from paracord and ran the ends through the open top of the bottle. We secured the paracord with tape and attached the carriage to the balloon with a carabiner. To ensure the camera was taking pictures constantly, we placed a rock over the shutter button and taped it down, holding the button down.
• Gathering data
  • Our group flew our balloon at Carpenter's Orchard to the area where the bioswale is located. We estimate the camera was approximately 130 feet above the ground, constantly photographing the bioswale and the landscape surrounding it. The camera took a picture every second, giving us a plethora of images to use for the map stitching portion of our project.
• Analysis
  • With the camera taking pictures at an interval of one photo per second, we were able to amass a library of almost 1000 images. We chose the four best pictures to stitch into the pre-existing satellite imagery of the area. Our final product, which is attached below, depicts the bioswale in near-infrared imaging. The purpose of the near-infrared function is to represent plant health and diversity. Overall, our flight was successful in providing us with the necessary imaging to accurately stitch together a near-infrared map of the area.

Results:

• What worked and what didn't?
  • The fin helped stabilize the camera carrying device we created. The carriage shielded the camera, but was also a holding device for it. Taping the rock down onto the shutter button helped maximize the amount pictures needed for a sufficient data. A particular challenge we faced was finding the right measurement of helium to put into the cloudbuster balloon. At first, we did not fill the balloon with sufficient helium to lift the camera. After the third attempt, we reached the appropriate amount so the line was pulled taut and resisted the pull of the person manning the flight.
• What did you learn?
  • We learned the best images are taken when the balloon is at higher altitudes. At a greater altitudes, the camera will capture a wider range of scenery and give us a clearer image of the bioswale. We learned to make sure the position of the balloon changed in the sky while walking around the bioswale so there was a variety in pictures. We still had some images that were slightly displaced, but the majority of our shots were usable.
• Actual Results
  • With the developed NIR images, we were able to infer that the bioswale is functioning well and in the manner it was intended for. When looking at the photo, it is apparent that the tributaries surrounding the bioswale have higher photosynthetic activity than the bioswale. The vegetation appears lighter in the developed infrared photos which suggests that they are healthy. The bioswale itself is healthy as well, and the size is effective.

Recommendations:

• Equipment
  • We would recommend the use of identical carriages for all groups every flight. The carriage we used was extremely effective, but to have accuracy with all projects would be favorable. The balloons and the harness line worked well, but figuring out how to effectively tape the string to the carriage was difficult. However, this was a challenge we overcame.
• Replications over time
  • Replications are important because it allows us to collect data from multiple runs, giving a greater variety in imagery and giving us the opportunity to capture images in different conditions. Flying the balloon should be replicated twice, then furthermore if necessary. Most of the times in experiments the first try is unsuccessful, so repetition is necessary. We noticed a few variables that provide potential detriments to flight such as wind. A strong wind makes it difficult to gather data as it can be hard to guide the balloon. The wind can also have an effect on where the pictures are being taken because it can blow the camera carriage around, giving us blurred and/or inconsistent imaging.
• Future directions (improvements or additions to the methods, additional studies this makes you think of)
  • There was little we could have done considering the time that was given and the events of the past 3 weeks at The Thacher School. Having said that, we could have used our time in a more effective way. We had a few tasks we could have used less people for and spared a few people for assignments that would help our group advance. When we didn't need to take the balloon out, we had to accumulate all the photos which in reality was a one person job, that was split up into three people.

Reflections:

Based on the images below it is clear that the Bioswale is having a positive impact on the area. We learned that through these photos, we can determine whether or not the bioswale is effective. The importance of balloon mapping with an NIR (infrared camera) is that other photo taking processes fail to show the photosynthetic activity, which shows how healthy the plants are. We think that measuring the water quality of the creek just below the bioswale and tributaries could have been an extra step in determining whether the bioswale works, but with the images we took we had a substantial amount of evidence to prove that the bioswale is healthy and doing its job!

Processed NIR images showing an NDVI rendering of the bioswale and surrounding vegetation-- areas of brighter colors (or brighter shades of grey) correspond to higher levels of photosynthetic activity (healthier vegetation)