Headwall Photonics Blog

The Eyes Have It...But Not Always

Posted by Christopher Van Veen on Thu, Apr 13, 2017

Humans have a marvelous ability to see and identify objects within what is called the visible range of the electromagnetic spectrum. That starts at roughly 380 nanometers and goes up to around 700 nanometers or so.

But there are things that researchers and scientists might wish to 'see' that fall below (ultraviolet) or above (infrared) this 'visible' portion of the spectrum. If you were a bumblebee, you could see into the UV range; a rattlesnake, you could see into the infrared range. Obviously (and thankfully) we're neither, but to see into these other ranges we need help. And why would we care about anything our eyes cannot see? Well, to take just precision agriculture as a key example, there are vegetative indices (VI's) that depend on seeing into the infrared ranges where the spectral signatures of chlorophyll fluorescence are detectable. Chlorophyll fluorescence is predictive of crop stress and vigor, so being able to see and quantify its effects can tell crop scientists much more than their own eyes can. 

DJI-MATRICE-600.jpg

Since we aren't bumblebees or snakes, we need tools to see into the nether regions of the spectral range. Hyperspectral and multispectral sensors do the work our eyes can't, and they do it very well. They collect, in the case of hyperspectral, a full spectrum of image data for every pixel within the field of view. Dozens of vegetative indices exist, with each using spectral data to discern answers to questions: Are there diseases on my crops I cannot see? Is my soil nutrient-rich? Are there invasive species I need to worry about? In the end, scientists concern themselves with finding answers to these and other questions rather than poring over complicated hyperspectral data cubes. In layman terms, you go to Home Depot not to buy a drill; you go there to buy a hole.

Hyperspectral and multispectral differ with respect to the amount of image data being collected. Hyperspectral is to multispectral what hundreds of bands are to a handful. With multispectral, you also may have gaps between the rather wide bands and what you want to detect with the sensor might not register. But hyperspectral represents hundreds of narrow and contiguous spectral bands, so if a certain spectral signature is there you'll see it. There are places for both multispectral and hyperspectral; if you know the spectral signature of the vegetative indices of interest and you're sure the multispectral sensor can capture it, you're all set. But much more common is the case where scientists do not exactly know where along the electromagnetic spectrum a key VI exists. Is it somewhere between 400 and 1000 nanometers (nm), which we call the visible-near-infrared VNIR range? Or is it in further up, between 900-2500nm (the shortwave-infrared SWIR range)? Indeed, missions may change over the course of the instrument's life, which means that scientists would opt for a combined VNIR-SWIR sensor capturing image data from 400 nm all the way up to 2500 nm.

Hyperspectral and multispectral imaging sensors are often 'line-scan' instruments, basically meaning they capture image data a slice at a time. The composition of all these slices (or frames) is a hyperspectral data cube, which can be several gigabytes in size. Post-processing software is very good at unscrambling this complex cube of data into meaningful answers, but just as important is aircraft stability. Since UAVs are quickly becoming the 'go-to' platform for crop scientists and others, making sure the craft is stable in the air is fundamental to making sure the data is orthorectified. In other words, not a casualty of a wobbling UAV. Fortunately, stabilized gimbals are outstanding nowadays, having the immediate ability to keep the sensor in its desired position no matter what the craft does.

Obviously, a UAV-based remote sensing system is a function of optics, electrics, and aerodynamics. Integration is an overlooked task, because many users assume that they can buy a UAV and a sensor and bolt the two together. Unfortunately, experience shows that such a piecemeal a-la-carte endeavor is likely to fail. Battery life comes into play, balance rears its head, and understanding the relationship between frame rate and ground speed can flummox anyone. Fortunately, though, companies like Headwall Photonics exist to manage this integration process. They understand a thing or two because they've seen a thing or two. They can recommend the right kind of UAV, take size/weight/power (SWaP) into consideration, integrate spectral sensors with other instruments such as LiDAR, and deliver turnkey, flight-ready packages that even bumblebees and snakes would have to admire. 

Tags: hyperspectral imaging, Airborne, Remote Sensing, Nano-Hyperspec

Nano-Hyperspec, PrecisionHawk Impress!

Posted by Christopher Van Veen on Wed, Jul 06, 2016

Steven Sexton is Technical Consultant at Aerial Imaging Services, LLC (Ephrata, WA). With broad availability of new UAVs and high-performance hyperspectral imaging sensors, Steven's business is a good one. 'Remote sensing' is the study of agriculture, climatology, geology, and infrastructure from airborne platforms. The amount and quality of image data the sensors collect is amazing, allowing scientists to make important decisions about crops, plant health, mineral deposits, and environmental trends.

Recently, Steven teamed up with Precision Hawk (Raleigh, NC) and Headwall Photonics to put one of these 'flying laboratories' into the air. Because the combination of UAVs and specialized sensing instruments is still 'new' to many users, ease of integration and great customer support from Precision Hawk and Headwall allowed Steven to get into the air collecting data-rich images of the ground below. Precision Hawk took care of many of the airborne issues while Headwall addressed the hyperspectral side of the application. Together, both companies helped Aerial Imaging Services reach a very impressive level of differentiation in a still-emerging business. The myriad of mechanical, electrical, optical, and aerodynamic considerations can be daunting, and Steven took to LinkedIn on June 28, 2016 to tell his story:

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I am going to shift focus to sensors today. I recently acquired a Nano-Hyperspec Sensor from Headwall Photonics and PrecisionHawk. This sensor is absolutely amazing, and is configured to just plug right onto the Lancaster Rev 4 and the Lancaster 5. This Plug and Play setup is how all of the sensors PrecisionHawk sells. Making it extremely easy to do a visual scan, land, change to a  BGNIR sensor and fly. They sensors scan at much higher resolutions then most multispectral sensors. Around here being at a higher altitude means not running into the trees lining fields, silos, buildings etc. I get 1.5cm per pixel at 100m or 329 feet AGL. I go lower for Lidar and thermal to 60m or 196 feet AGL.

Now this may seem a little high but with the higher resolution sensors I got from PrecisionHawk, it just made sense, less worry and more time to just watch the Lancaster do its thing. It also means I don't have to make as many passes over a field like I would at lower altitudes. Now I haven't heard anyone say the resolution of some of the newer multispectral sensors that recently have come out or those that I may not know of. If you use one of these, and it gets as high of resolution, please, either leave a comment and share your results or message me so I can add that information to this article. I want to give everyone a fair shake here.

steve_sexton.jpgNow back to the Headwall Photonics Nano-Hyperspec® sensor. This unit is a little heavier than most of my other sensors, The LiDaR is about as heavy. The reason for the extra weight is a 500gb SSD drive attached to it. It also has a network cable interface to hook to your computer or laptop. Please read the manuals that come with it, it will save you a lot of headaches trying to figure out how to access the SSD on the sensor. You can find general information at the Headwall site here.

The customer service from Headwall is absolutely amazing. I decided to update the Nano driver software and missed one step and wound up not being able to access the data. Now this was totally my fault, I kind of went in blind to do the update.

Greg Chenevert from Headwall was extremely helpful and had me try a few things. These didn't work, but Greg spent time trying to help me get things going and guaranteed that they would get it back up. He put me in contact with one of the companies programmers, I gave him remote access to my system with the Nano hooked up and running and he had it all set up, reconfigured and doing imaging within probably 15 minutes at the most. Now I don't know about the rest of you, but most companies don't even come close to the customer service of Headwall and PrecisionHawk. They went way above and beyond to get the sensor working so I could do my job.

The unit itself is not that big, it is the bracket and connectors for the plug and play that make it seem larger. On average I can swap out a sensor and battery in about 30 to 45 seconds. The battery only lasts for about 35 minutes with the heavier load, but I get some pretty amazing images with it.

Headwall has software that accompanies the sensor that are very useful and allow you to transfer the files to a local drive on your computer or laptop. You could even transfer it to a USB drive if you have one that can hold the amount of data you get. There is also an option to view the data in NDVI, now this can be done in the field if you so desire. I usually just bring it back to the office and process it there and add it to other data sets I have gathered on that particular job. It does make the farmer happier if you can show it in the field.

Lancaster.jpgWhen I first started I was unsure of which sensors I should purchase. I imagine several of you have or had the same issue. I determined that if I only get the sensors for agriculture then I am going to be very poor during the winter months. I decided to add the LiDaR, thermal, and the HeadWall Nano-Hyperspectral sensor. This gives me the ability to do other types of work during the non growing season. I also don't mind travelling to a location or even going to another area for several weeks at a time so this also opened up income opportunities.

The data is only as good as your sensors are. Sure the higher quality imagery costs a bit more, but, it also means the data is going to be more precise. Combined with the DataMapper Algorithms you get a very complete package from one source.  

Tags: Remote Sensing, UAV, precision agriculture, Nano-Hyperspec, PrecisionHawk