Mount Umunhum Restoration Project

 "The Box" on Mount Umunhum Summit is an 85.5 ton GE Radar Antenna used to detect approaching aircraft during the Cold War.

 "The Box" on Mount Umunhum Summit is an 85.5 ton GE Radar Antenna used to detect approaching aircraft during the Cold War.

Sandis Civil Engineers

Client: Midpeninsula Regional Open Space District

Project Objective: Provide base level topographic map for planning phase of restoration project.

Operator: Andrew Chafer, PLS, CFedS ;Senior Project Surveyor

UAS: AeroTestra MK09 Aerial mapping System

Location: Mt Umunhum,

Date: February 2015


Project Description: Mt Umunhum, known by local residents as “Mt Um”, is the fourth tallest mountain in the Santa Cruz mountains. It is identified by a 5 story cement tower “The Box”, which is an 85 ton radar antenna used to detect possible threats during the Cold War. The site is now being restored to allow public access.

Environment: The summit of Mt Umunhum is largely inaccessible due to steep terrain or dense undergrowth. This would make traditional survey methods difficult.

Deliverable: For the planning phase of the project, Sandis was asked to provide a planning level topographic survey as well as a scalable orthophoto of the site.

Topographic Survey

Flight Details:

  • Number of flights: 3 (2 on the summit @78 acres; 1 over the Guadalupe Creek Overlook @17 acres)
  • Flight Altitude: 100m AGL (above ground level)

  • Image Overlap: 80% overlap  70% sidelap

  • Total area covered: 100 acres

  • Flight Time: approx 15 min per flight

  • Ground Sample distance: 2.67 cm

  • Pictures taken: 417

  • Control points: 18 on the summit; 6 on the Guadalupe Creek Overlook

Surveyed with the Leica 1200 GPS Rover


Advantage for Sandis using AeroTestra MK09 UAS for aerial survey: The summit is closed to the public due to hazardous materials and unsafe partially demolished structures of the former Air Force station. For this reason there was an advantage to using UAV to provide the required topographic data while limiting exposure to hazardous materials or conditions.


Comparative analysis versus surveying method:

Cost Savings

Traditional Survey in an area like this would be difficult given the accessibility of the area and the dense growth that would obscure line of site operations. An estimate of the man hours required to survey this site would have been approximately 5 days. During this time, about 4000-5000 points would be surveyed. These would be limited only to the areas that were accessible. The labor cost for this portion alone would be over $20K.

Manned Aircraft Survey would be the current method for mapping this site given  industry standards. This would require contracting a photogrammetry service to perform the flight, deal with image acquisition and 3D reconstruction. Often these are three different skill sets required to produce the final 3D topographic model, DEMs, and orthophotos.
The same 24 control points would be required as in the sUAV survey. From the time of initiating the project to the receipt of deliverables is typically 6 weeks to 2 months at a cost of $14K. This does not include setting the registrations or formatting the deliverables into a finished set of documents for the end user.

Small Unmanned Aerial Vehicle Survey using the AeroTestra MK09 multi rotor mapping system allows for setting registration points and image acquisition to take about 6 hrs.  Once back at the office the images are uploaded to Agisoft Photoscan for 3D reconstruction. By the next morning a complete, geo-rectified 3D model, digital elevation models and orthophotos are waiting. Andrew estimates the cost of the entire operation to be approx $4500.