Flying a Drone in Remote Nevada

Welcome to the first edition of my monthly newsletter… the Digital Mapper! I’m Michael Detwiler, and I work as an Associate Photogrammetrist at Wood Rodgers. I’ve traveled quite a bit for work in the past decade and contributed to many challenging projects, in many interesting places. After over 17 years of experience, I am looking forward to sharing more about aerial mapping, land surveying, and unmanned aerial systems (UAS) with you through this newsletter. 

I enjoy reminiscing with former and current colleagues about past adventures. However, I have always wondered if anyone else would find these stories amusing. I had an idea to create a monthly newsletter, with the goal of simply highlighting a recent survey project, and sharing the story and challenges it presented. The focus of the Digital Mapper is to show how cool survey projects can be – especially because they are outside, in the field, with high tech gadgets! By telling my story, I also hope to inspire young professionals or students to pursue the career of a Photogrammetrist and/or Land Surveyor.

Corridor Mapping in the Remote Nevada Desert

Over the past few months, I have been working on a gas pipeline mapping project in north central Nevada. The site is located about 30 minutes from any town, so while it’s not completely isolated, it was a long 3-hour drive from the office. This means do not forget any equipment back at the office! And if something breaks, you have to find a way to fix it and make it work!

There are many aspects to this particular project, including survey, environmental, and civil engineering components. My role was to oversee the capture of aerial data using a fixed wing drone to produce a planimetric and topographic map for engineering route design. 1-foot contours were generated for accurate slope and terrain analysis. Horizontal locations of improvement features and encumbrances along the proposed pipeline route were also mapped. Despite the site being in a remote valley, the route is proposed to be along a well-used gravel road with many utilities and easements alongside. Therefore, accurate horizontal mapping for clearances was imperative!

Weather Forecasts Are Not to Be Trusted

We received the notice to proceed from our client in late January and mobilized to the site in February. A survey crew had set aerial control targets in advance and we anticipated two days to complete the aerial data collection.

Winter weather is not very nice for surveying in Northern Nevada in February. On day two, we had an abrupt change of weather as snow flurries moved into the northern end of the valley and halted our progress. Live radar maps on our phones showed this storm as the only snow precipitation within a 100-mile radius! We felt so blessed mother nature chose us with our very own snow storm (insert sarcasm!).

We retreated back to town and the hotel, and hoped to finish up the next day. Upon driving back out the next morning, the sun was shining. At the south end of the valley, there was no snow present on the ground. It should have been a good day for flying. But 25 miles later, at the northern end of the project site, a good three inches of snow had fallen overnight. Based on the unreliable forecast, we were forced to temporarily postpone the project to allow for warmer temperatures to melt the snow off. It ended up being a 1-week delay before we could return to the site and finish the aerial survey.

Data Processing Challenges

I have worked on larger aerial mapping projects than this particular one, using imagery from cameras aboard both manned and unmanned aircraft. However, this particular project presented its own unique set of challenges.

The largest drone project I have worked on required approximately 11,000 images to map 6,000 acres. In this case, the pipeline data-set ending up being about 5,000 images. But due to the linear nature of the data-set, I found that trying to process all the images at once was futile. Despite having ample survey control on the ground and post-processed kinematic (PPK) geotagged images, the photogrammetry software struggled to make the necessary adjustments across the vast linear distance.

A lot of trial and error and theories were tossed around, but in the end, the most successful approach was to break the corridor down into twelve, two-mile sections to perform the photogrammetry adjustments. Then, we merged the segments all back together, before generating the final ortho-image and digital surface model. Whew… a lot of brain cells burned in that process.

What Did We Learn?

Larger projects present more challenges, so sometimes it’s best to break it down and solve these problems in steps. This project presented some of the toughest problems to work through. But it goes without saying - there’s a little pride once a job is complete and delivered.

If time and schedule allow, it’s best to wait for a suitable, long weather window before scheduling aerial survey flights. This, more often times than not, isn’t the case. A client says “go” and expects you to be on-site the next day. If you can communicate clearly, how more successful the project can be, given optimal circumstances, the client is usually amendable. In this case, the client was understanding knowing it was February and the middle of winter. They knew the crazy Nevada weather well, so they accepted the delay without issue.

Using a UAS was a better choice on this project because of its flexibility. The corridor route changed three times over the course of the preliminary design. It was relatively easy to re-mobilize a pilot and survey crew to capture the new data, compared to re-mobilizing an airplane. Mobilizing an airplane would have been more time prohibitive based on airplane schedule, travel distances, and weather restrictions. Often times a UAS can slip in under cloud layers and capture suitable imagery where a manned aircraft flies at an altitude above clouds, obscuring ground features.

The Digital Mapper is written by me, Michael Detwiler, with a new release at the beginning of each month. Please feel free to comment and/or reply directly. If we are not a connection on LinkedIn and you enjoyed this newsletter, lets please connect to share the story!

I can also be contacted at mdetwiler@woodrodgers.com

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