For decades, farmers and agronomists have anticipated that remote sensing would someday be relied on to contribute valuable data for crop management.
High-quality imagery obtained by airplanes has been readily available for about 10 years. The main disadvantage of aerial imagery has been the cost—typically $1.50 to $2.50 per acre. This is a reasonable price, but in times of low commodity prices, it is not easy to convince growers of the value of well-timed aerial imagery. Another disadvantage is the need to assemble a minimum order of about 1,000 acres. We used aerial imagery flown in August during a dry spell to delineate the moisture-holding capacity of lighter textured soils for clients who have variable-rate planters. It’s hard to beat aerial imagery for this application.
Valuable But Time-Consuming Tools
In my opinion, much of the excitement around the potential for UAVs to deliver real-time imagery has been hype. Don’t misunderstand me. I think UAVs will be valuable tools for farmers and agronomists, but collecting and processing imagery is time-consuming.
It is also a challenge to find the perfect time to fly a drone. Wind speed needs to be less than 10 mph to 15 mph depending on the platform you are using. If you are planning to use the imagery for NDVI, then the flight should probably occur between 10 a.m. and 4 p.m. I have noticed a pattern—the best conditions for flying a drone usually occur on the weekends or evenings when employees are not available to work.
The time required to process imagery has been another challenge. Much of the imagery capture occurs during the busiest time of the growing season. Agronomists are assessing stands and addressing weed control and disease and insect pressure. It is very difficult to pull away from these primary duties and send someone to fly a drone.
Advancements in automatic processing have been made where data are streamed to a cloud system and the processed imagery is delivered shortly after the flight has ended. I have not tried this service, but I wonder if 3G/4G internet access is actually able to upload and download the amount of data necessary to accomplish this in the middle of nowhere.
Opportunities With Satellites
I have been looking at 5-meter satellite imagery for a couple of years and have found that useful imagery is available from June through September. Our average field size is 25 acres, so imagery needs to be 5-meter resolution or better to be useful. Cloud cover and the previously infrequent (about two weeks) acquisition period from one satellite have caused this to be an unreliable source of good imagery in the past.
It appears that satellite imagery has undergone a quantum improvement in frequency and reliability during 2017. Apparently, a few new satellites have come “online” in 2017. We had two vendors offer access to satellite imagery for all of our clients’ fields for a reasonable package price. We decided to take a look at the service from one company. After signing a service agreement, one of our interns spent a few days uploading shape files and naming fields to get everything into the system. It didn’t take long to start seeing recent 3- to 5-meter “crop health index” images that represent the fields really well. To date, we have received a new image about every seven days. So far, the images have been helpful in identifying the extent of apparent nitrogen deficiency in corn and confirming the subsequent recovery of deficient areas after sidedress nitrogen. We plan to use the mid- to late-season images to help fine-tune our yield predictions.
If you have not tried a satellite imagery service in 2017, then I recommend that you check out one soon. I think you will be impressed.