Unmanned Aircraft Systems (UAS) (also called Unmanned Aerial Vehicles or UAV) hold several tactical and practical advantages over crewed aircraft. UAS, or drones, can fly in weather where it would be imprudent or dangerous to send up a crewed aircraft. However, law enforcement agencies do need to take precautions to deploy in extreme weather. The St. Cloud (Minnesota) Police Department has a wealth of experience with cold-weather missions, and Officer Alec Elness and Commander Martin Sayre shared their practical approaches and considerations for deploying in cold weather. All temperatures are given in Fahrenheit.

The weather in central Minnesota can be challenging. “Our average annual temperature is sadly 42 degrees,” says Commander Martin Sayre. “Another depressing statistic is that the average number of days in St. Cloud below freezing is 177/365. Our record low was 49 below zero, but we’re always going to see a few days of 30 below zero.”

Officer Alec Elness says that considerations for cold weather can be broken down into three categories: (1) equipment concerns, (2) operator concerns, and (3) other obstacles.

The first consideration is the battery. “Depending on the platform you are operating, we know that batteries interact badly. Most enterprise drones have some self-heating capability. If you are in the Northern climates, self-heating systems are necessary. As long as the battery is warm, it’s good,” says Officer Elness. If the voltage in any of the system batteries drops below a certain level, the system can experience a catastrophic failure. This includes the batteries in the controller, the tablet, or the drone itself.

The second consideration is operators. Operators need to be appropriately clothed or protected for the duration of the operation—or, as they do in St. Cloud, you can rotate operators into the weather. You can house an operator in a warm vehicle, but only if they can maintain visual line of sight with the drone. Operating drones requires fine motor skills, and gloves can interfere with operations, so St. Cloud suggests having operators practice with gloves. Commander Sayre added, “From a command perspective, one of the things we’re trying to implement now is a good streaming system so that we can have visual observers inside a climate-controlled vehicle watching the footage who know what to look for with a one-second lag in time who is actually spotting items of interest.” In this set-up, the operator is simply responsible for the drone and an observer is reviewing the footage for leads.

The third consideration is other obstacles, specifically atmospheric conditions, which present unique challenges for drones. If it’s snowing, operators can experience line-of-sight concerns. If it’s windy (and it’s usually windy in Minnesota), you have to take wind chill into account. Snow and sleet can cause rotor issues as well. Officer Elness recalled a particular operation: “One operation two years ago, we had a freezing fog so we had rotors ice over. Most drones are not operating right at their payload, so usually they can operate with an increase, but you will not get any warning that the rotors are icing up and the weight of the drone is increasing. You’ll start to have handling problems but there is no way to know that the payload is increasing.” So how do you prepare for atmospheric challenges? “Do a test flight in inclement weather and check if the props are icing, is visibility good at that altitude, how is the battery, all of that stuff. It’s not always possible in a dynamic emergency.”

Winter operations have additional considerations as there are some limitations on what the drones and operators can handle. “Normally,” said Commander Sayre, “we wouldn’t fly a UAV at 25 below, though we would if there was a lost child or other dynamic emergency, but at those temperatures we are putting the asset at risk.” Officer Elness added, “I am thinking of every planned [SWAT (special weapons and tactics)] and I can only think of one pre-planned incident where we did not fly due to extreme winds. Air temperature was 20 below and winds were upwards of 25 mph. You can almost always deploy with proper planning.”

However, there are advantages to operating in winter conditions. “A big plus to operating in the winter and the late fall and early spring is that the trees are defoliated,” said Officer Elness. Commander Sayre added, “The advantages to loss of foliage are significant and so are the FLIR signatures.” FLIR is the infrared camera system on St. Cloud’s drones. Tree leaves give off heat signatures that create visual noise as well as blocking visual access. When the leaves are down, heat signatures stand out in greater contrast to the surrounding environment. St. Cloud even discovered during practice and incident review that the FLIR technology can see heat signatures left in fresh footprints in the snow. “The heat signature remains for 15–20 minutes and you can see a cookie-crumb, Pac-Man type trail,” says Officer Elness. This can provide crucial information in case of a missing child, student, or elderly resident who has wandered out into the weather.

“The nice part is that where your FLIR is giving you the best data is the environment in which it’s the most necessary,” said Officer Elness. “It’s riskier to operate, but the payout is better in life-threatening circumstances like an Alzheimer’s patient. Otherwise the missions themselves don’t change. A missing kid in the summertime won’t see drone results versus a search team. In the winter, the UAS can help protect search teams.” Both Commander Sayre and Officer Elness emphasized the importance of practice and planning ahead of a dynamic event in winter conditions. Not everyone has 177 days below freezing in which to prepare.

Sarah Estill
Social Science Analyst

For more information on Unmanned Aerial Systems (UAS), see Roadmap to Implementing an Effective Unmanned Aircraft System (UAS) Program and Drones: A Report on the Use of Drones by Public Safety Agencies—and a Wake-Up Call about the Threat of Malicious Drone Attacks.

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