Field Notes 2: Sensor Comparison

Intro:

Despite what a lot of people think not all UAS sensors are created equal. There are a large variety of sensors that you can get for just one single UAV. In this post I will discuss the differences in the four sensors we used on three different UAV platforms flying relatively the same mission.

Study Area:

We were at Purdue Wildlife Area,8000 IN-26, West Lafayette, IN 47906. Weather was a perfect 70 degrees Fahrenheit with winds out of the SSE at 3 MPH with no gusts with clear skies at 400 feet 
AGL. We flew the Mavic 2 pro at an altitude of 400 feet AGL and the camera set at 90 degrees down.

Methods:
My crew and I went to fly a smaller section of the same field we flew in "Field Notes 1". We set out five GCP's. One in each corner and one in the middle, starting in the north east corner working in a clockwise direction ending with the middle GCP. We picked the GCP's in the opposite order to make sure that when we got back to the lab the data would be easily collected and the GCP's would be labeled correctly.

We flew a mission with three different UAV platforms with a total of four different sensors, which are labeled in the "Discussion" section. The order in missions went H520, M600, M600 Olympic lens, then Mavic 2 pro. My crew flew the Mavic pro 2, we made sure to get plenty of overlap and to fly past the boundaries of the area we wanted to cover to make ensure that we had clean edges and boarders. Flying at 91 meters (300 feet) at 8.9 meters per second we completed our mission in 9 minutes. With no mistakes in the mission.

Discussion:

The specs for each sensors on each platform are labeled below. If you want to find more information about the sensors then just click on the link and it will take you to the companies site of each sensor for all of the more in depth specs for all uses.

Sensors:

Mavic 2 Pro Hasselblad: 20 Mega Pixel, 77 degree FOV
https://www.dji.com/mavic-2/info

M 600 Olympus: 16 Mega Pixel, 84 degree FOV
https://asia.olympus-imaging.com/product/dslr/mlens/12_20/spec.html

M 600 Stock: 16 Mega Pixel, 72 degree FOV
https://www.dji.com/zenmuse-x5/info#specs

H 520 E-90: 20 Mega Pixel, 90 +- 3 degrees FOV
https://www.yuneec.com/en_GB/accessories/cameras/e90/specs.html

Like I said earlier not all sensors are the same and not just any sensor can be best for every job and below are just a few examples of the differences that can occur in relatively identical missions.

Figure 1:

Below you will see that there are a few differences in the four orthomosaic images collected from the four missions flown. The first difference that is probably the most noticeable is the difference in area covered by the E-90 lens, you can easily see the entire west tree line and even see the west pond. This is do to the wide opening lens. This may seem like a benefit, but as I will point out later there are downsides to this. The image also is very dull and lacks true representative color because there are additional settings that were not changed that would allow for a more vibrant image.

Figure 1

Figure 2:
Looking at the map below you can see two sections that are blocked off in red and highlighted. These are the two sections we will be discussing. In the top highlighted section on the map you can see the four different layers of the four different missions flown. In the orange layer, the E-90 sensor, there is a large amount of gelling happening with the images. This causes the map to turn out blurry in that section. That is why you see large pyramid like shapes outside of the other layers of the map.

On the left hand highlighted section we can clearly see the pond that I brought up earlier. The unique part of capturing the pond in this mission that neither myself nor anyone else in my crew had ever seen before was that you could actually see the water. In every other situation I have ever encountered the water shows up as either a white or black hole. This is because it is so hard for the software to get a point that it can use over and over again sense the water is always moving.

Figure 2

Figure 3:
The Mavic 2 Pro is the smallest UAV and smallest sensor out of all the platforms and missions flown that day which made some members of other crews think that it would would under preform compared to the others, however this couldn't be farther from the truth! The Mavic flew the fastest mission and had the clearest orthomosaic out of all of them. In the images below we are comparing the detail in our vehicles. The Mavic has hands down the most clear image of the vehicles. The members of each crew were moving around throughout each flight so it is hard to be able distinguish people from other objects. With that being said it is easier to see the difference with the Mavic. In front of the Black SUV, the middle vehicle, you can clearly see a crew member sitting on the ground with his legs bent up.

Figure 3

Conclusion:
Before you fly any mission you need to make sure you have the best sensor for the job and for your UAV. Each mission will need unique setting and possible unique sensors. As you can tell every sensor has its advantages and disadvantages. Which is why you need to do your research on the mission itself so you can be best equipped to produce the best data for yourself or for your client.