Drones are revolutionizing myriad facets of business of around the world — either by doing new jobs or finding new ways to do existing ones. But for most operations the value of the drone is not in its ability to fly, but in the sensors they’re able to carry.
With that in mind, let’s take a look at some of the most widely used drone sensors, and some key considerations you should keep in mind when selecting them for your business.
Visible light (RGB) drone sensors: The eyes have it
The most common — and most affordable — sensor being used is obviously the RGB or visible light sensor. Because their imagery is so familiar it is also the easiest to use and interpret, requiring no specialized techniques or training to use. Visible light imagery is also very easy to gather and convert into 2D maps and 3D models using Pix4D’s photogrammetry software.
While these may seem rather ordinary, there are a couple of things you want to keep in mind when deciding which is right for the data you want to capture. First is resolution — simply the number of pixels on the sensor, and the size of image you’ll be saving. Lots of off-the-shelf solutions out there today are capable of 4K images and video or even better, so for most industrial inspections finding a high-quality solution has become fairly straightforward.
Another thing to consider is zoom. Most off-the-shelf drones on the market have a fixed field of view lens, so the only way to increase the size of your object of interest in the screen is to fly closer to it. This is something to consider when you’re defining the data capture requirements you need in order to satisfy your business case — think of the smallest thing you’ll typically need to be able to see clearly, and how close can the drone get to that object.
If you’re more concerned with wide area viewing of large areas a camera with a wider, fixed, field of view will do just fine. But, if you need to be able to see the individual nuts and bolts that make up connections on electrical towers — and the drone needs to stay outside a specified safe approach distance — then a zoom camera may become necessary.
Now, it’s worth taking a moment to differentiate between optical and electronic zoom. Most drones do have electronic zoom to a greater or lesser degree, but what I’m talking about here is optical zoom. Digital or electronic zoom just enlarges the pixels in the image, effectively reducing the resolution on your object of interest, whereas optical zoom allows you to stay a safe distance from you object and still get a full resolution image when zoomed in.
Take the following three images for example. A full resolution image at safe approach distance from energized lines may not give the operator the needed details (top). A camera that only provides electronic zoom (middle) may make the object big enough, but at the cost of losing the ability to read markings and inspect components. Optical zoom (bottom) maintains the full image resolution, even while zoomed in.
The next thing to consider is light-handling capability. If you’re an aerial photographer or videographer, or doing photogrammetry, you’ll probably be taking your images with plenty of good lighting, so it won’t be an issue. But those involved with public safety or emergency response work should look into the light handling capabilities of the different camera options that are out there — some will work just fine in an urban or suburban setting with the artificial lighting available, while others lose their utility after sunset.
Visible light imagers have another weakness that is so glaringly obvious that people often overlook it: they only see what your eyes can see. Fortunately, infrared imaging sees what your eyes can’t.
Thermal (Infrared) drone sensors: Making the invisible, visible
Infrared, or thermal, cameras detect and display the heat energy that comes from the surface of objects and make images from the differences in that radiant heat energy. This gives you images of energy that is invisible to the naked eye, giving you awareness of potentially problematic conditions that are first betrayed by abnormal heating, or a lack of emitted heat.
Because thermal imagers see heat, not light, they are not dependent on having a certain amount of visible light in order to work effectively. But it goes beyond that — thermal imagers are not affected by the amount of ambient light in a scene at all, so they can work at high noon or in total darkness.
In industrial settings thermal imaging is used for all manner of diverse applications like roof investigations, solar panel inspections, looking at electrical transmission and distribution lines, and checking on piping and chimneys at oil and gas facilities. In all of these use cases, potential problems will often first be shown with a heat differential that you can see with a thermal camera. For instance, if there’s water trapped in the insulation under a membrane roof, that can cause a temperature differential on the surface of the membrane.
So, things to consider with infrared imagers. First, again, will be resolution. Generally speaking, the more pixels the better, but the thermal cameras used on drones are typically much lower resolution than what you’re used to seeing with visible light cameras. The most common resolutions are 320×256 or 640×512. A 320×256 resolution thermal camera is just as technically capable as its higher resolution cousin, with the one exception being photogrammetry — making thermal orthomosaics with a thermal camera will generally require a 640-resolution camera.
Cameras with very low thermal resolution, like the 160×120 resolution image on the top, provide neither enough image detail, nor temperature separation for effective inspections. A 640×512 thermal camera (bottom) lets the operator make out conductors, insulators, and subtle temperature differences from a safe distance.
Another consideration is whether the camera is what’s commonly referred to as being radiometric. That term is often used rather loosely — all thermal cameras are radiometers — but what people really want to know is if they can be used to get a temperature measurement, or to do some sort of thermographic analysis in post processing.
A specialized form of thermal imaging that is less known is called Optical Gas Imaging, or OGI. OGI uses cooled infrared cameras that are filtered to be able to see hydrocarbon gasses. Environmental regulators commonly use these to check on a petrochemical operator’s compliance, but the producers also use them to guard against lost product and potential fines.
Combining drone sensors: More is better
While it is often the wisest course of action to start with a single type of imager and prove the profitability of that use case before investing in another set of drones and cameras, understanding how visible and thermal imagers can work together is important to fully appreciating their value. Combining the two will not only allow you to see more things but will also allow you to operate effectively in bright sunlight and total darkness.
Public safety agencies — whether they’re fire departments, law enforcement, disaster response, or any number of other specialty agencies — often require a combination of sensors, depending upon the mission at hand. A visible light or RGB sensor would be the go-to for law enforcement agency while supporting a tactical team responding to a hostage situation.
That same agency may be called upon after dark to search for someone lost in the woods, or an elderly person who has left a care facility at night and gotten lost. In that case, a thermal imager would be a better selection as the active sensor because the primary goal is the detection of a person after dark and scanning a large area quickly and find heat signatures that can be approached by other personnel.
Buy Right, Buy Once
As always, Skyward’s recommendation is to thoroughly understand the business problems you’re trying to solve by defining your use cases and ROI before buying expensive hardware. Starting small and scaling after you’ve proven your initial use cases is foundational principle on which to build a drone program.
If you have any questions or need help when trying to decide which sensors are right for your program, please reach out to Skyward — our Professional Services experts are here to help you make the best choices for where you are now, and where you’re headed.