Selecting a Drone to Meet Your phenotyping Needs:
As drones have become better, less expensive, and easier to use, more researchers have been incorporating them into their trial assessment programs. The new generation of drones are bringing more capacity to assess new and previously inaccessible traits such as wheat head count, flower/fruit counting and classification, and phenological stage detection.
Many interesting traits can be assessed with multi-spectral sensors, but many of the most exciting and impactful traits that leverage deep learning tools are extracted from imagery captured with high resolution RGB cameras.
So, if you are thinking about leveraging drone technology to extract new traits to enrich your trial data sets, here are 5 drone features to consider for High-throughput Plant Phenotyping (HTPP).
1/ 5 drone features to consider while selecting a drone for plant phenotyping
Pixel count is very important for many of the most interesting and important phenotyping operations. More pixels create higher resolution to be able to classify and count small features in images such as counting thousands of heads of wheat in a plot. Generally, a research grade drone starts at 20 megapixels (MP) like on an Autel Evo II Pro or DJI Phantom 4 Pro V2. Sensors up to 100 MP are available for drones and allow higher resolution at higher altitudes which can help shorten flying times.
- SENSOR SIZE
Pixel count alone does not tell the whole story. Sensor size is even more important than megapixel count for phenotyping.
Resolution without an acceptable sensor size can be misleading. Larger sensors can have larger pixels which allow each pixel to capture more light and thus create a sharper image. With smaller pixels, less light enters each pixel and if there is not enough signal per pixel, cameras “bind” the pixels together reducing the functional resolution. An example that often confuses people looking at drones on the market now is:
- The DJI Mavic 2 Pro has a 1’’ sensor with 20MP thus a pixel size of 2.4 µ
- The DJI Mavic 2 Enterprise Advanced has a 1/2’’ sensor with 48MP thus a pixel size of 0.8 µ
Even though the Enterprise Advanced has a 48mp camera, the small pixels size actually yields images less useful than the larger sensor 20mp on the Mavic 2 Pro. Thus, larger sensors are particularly important for advanced deep learning phenotyping from drones for things like plant count or flower/fruit counting and classification.
- FIELD OF VIEW
There are trade offs around senor field of view (FOV). FOV and altitude define your global image footprint. A narrow FOV generates crisp images better suited for fine grained detail required for counting and classification deep learning. But with a smaller footprint you will need to take many pictures of a field (ei higher overlap) which will take more time and data storage space. For phenotyping applications on objects that have significant height or area (corn or tree crops) this smaller FOV also reduces geometric distortion caused by rendering a 3D object in 2D. So, for most detailed applications, a smaller FOV is preferred for plant phenotyping.
- OPTICS QUALITY
High quality optics yield images with higher sharpness, less distortion, less vignetting, and less chromatic aberration. Unfortunately, there are rarely metrics in specifications that allow you to assess the optics quality of sensors. For drones, unfortunately, all you can use as a guide is price. The higher the quality of the optics, the higher the price. Hasselblad and PhaseOne are 2 sensor providers that generally use high quality optics, but there are many others too.
- SHUTTER TYPE
Shutter type also affects image acquisition. Here are the 3 main types of shutters:
- sensor with rolling shutter and a mechanical shutter (the best)
- sensor with rolling shutter and electronic correction (the worst)
- sensor with global shutter (often available only for low-resolution sensors)
So, how does this boil down to the decisions you will be making on which drone best fits your needs?
Many research teams we work with select an entry-level research drone to get started quickly and then move to the advanced drones when they have a season or two of experience. But others realize the added impact that a more advanced drone can bring to their program, want to realize that value quickly, and will start with an advanced drone configuration.
2/ Global costs estimation of drone equipment options in 2022
Below are some examples of the rough cost of each equipment option and some of the systems we’ve had the best experience with.
- Entry-level Research Grade Drones – fixed sensors:
- Compatible traits: You can extract plant counts, flower assessments and head counts for larger headed crops like sorghum and sunflower with the fixed sensors on each of these drones. The resolution is not adequate to recommend for the higher resolution requirements of wheat head counting or small berry counting and classification.
- Price: These drones have fully integrated sensor controls and roughly costs 2 000$ after adding the extra batteries and accessories which we recommend for phenotyping usage.
- Advanced Drones – accommodate multiple sensors:
With higher resolution and larger sensors, you can fly at higher altitudes and fly faster and still acquire higher quality images in less time. These drones can carry multiple sensors which can be swapped in and out depending on your needs. This provides flexibility but can make operating more complex because the sensor and the drone are often not integrated. We currently use the DJI Matrice 300 and are very satisfied with its performance, flexibility, and ease of operation. The Matrice 300 costs roughly 10 000$ for the drone alone. Then you will need to add the cost of a gimbal and cameras. For the RGB camera options that really make these drones capable of delivering unique traits, here are several of the most common sensors:
Technical Specs Of The Sensors:
Overall, you need to determine the traits that will add the most value to your research programs and select the right tool for the job.
If you want help thinking through which traits are accessible and which drones and sensors are best suited to your specific needs, simply find a time on our calendar below and we will be happy to discuss your options and help you make the appropriate choice for your needs and budget:
Let Us Help You Select The Best Equipment For Your Needs
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