CopterSonde

The CopterSonde is an uncrewed aerial system (UAS) developed at the Univeristy of Oklahoma for the observation of lower atmospheric conditions. Dr. Tony Segales (OU-CIWRO) is the main developer of the system, and continuous to work in the BLISS group as the engineer improving and supporting this system and expanding capaibilities generally. You can read about the detailed technical background of the CopterSonde in Tony’s AMT article and in the US Patent documentation. The CopterSonde has undergone NOAA Airworthiness tests, and is cleared to fly on NOAA projects. You can check out this story for history and information about the construction of the Coptersonde. Below, a summary information brocure about the Coptersonde and its specifications is available.

Left, CopterSonde is piloted against the sunset. Right, the CopterSonde with main shell components, which are 3D printed, indicated. Instruments reside in the front shell, or ‘scoop’ part of the CopterSonde.

Features Designed with Meteorology in Mind

The grey quad-rotor Coptersonde sits on a light wooden benchtop. The instrument scoop is pointed toward the camera.
Temperature and relative humidity sensors are housed in a modular aspirated scoop that can be detached and independently calibrated to ensure measurement accuracy. Measurements of the wind speed and direction are obtained using the attitude data from an internal inertial measurement unit and compass.

Tried and Tested

A direct numerical simulation flow field is shown in a rainbow of colors deforming around the copter, which is positioned perpendicular to the viewer.
The CopterSonde UAS has been successfully deployed during several field campaigns in diverse locations and under a variety of meteorological conditions. Locations have included central Colorado, Finland, and central Oklahoma.

Precision Meteorological Measurements: Available on Demand

The original CopterSonde UAS was designed with the express purpose of sampling the thermodynamic and kinematic state of the lower Earth’s atmosphere, with a focus on vertical profiles in the planetary boundary layer. It provides the same information as a rawinsonde, but with much more control of its sampling location. Development began in 2016 for the NOAA funded EPIC (Environmental Profiling and Initiation of Convection) field campaign and development has largely continued through support from the National Science Foundation and the University of Oklahoma. The initial design has undergone considerable modification and the CopterSonde UAS is now capable of adaptative atmospheric sampling, real-time data processing and dissemination, longer flight times, and better data quality.
Our goal in developing the CopterSonde UAS has been to provide a sensor platform for lower atmospheric sampling that is easy to deploy, delivers reliable data, and facilitates adaptive sampling.

Sample Data Collection

The meteorological community has recognized the need for accurate measurements within the planetary boundary layer with sufficient spatial and temporal resolution for assimilation into weather forecast models and to improve forecasters’ situational awareness of prevailing conditions.

A skew-T log-P diagram and hodograph diagram showing coptersonde data from the Washington, OK Mesonet site.
These skew-T log-P, hodograph, and time-height cross section figures show some of the deliverables of the CopterSonde UAS. The measurements in the time-height cross section panel are from the CopterSonde UAS during a 24-hr experiment in Central Oklahoma. The CopterSonde UAS also measured pressure, humidity, and wind during this period.

A time-height cross section is shown in blue-purple-yellow shades depicting the boundary layer temperature evolution.

Key Features of the CopterSonde UAS

The current version of the autopilot code runs a set of custom functions added on top of the original ArduPilot code by our developer team. Some of the CopterSonde’s key features are:

  • Smart battery management and a high wind failsafe: these functions evaluate the potential risks automatically while in flight. The CopterSonde can trigger Return-To-Launch (RTL) by itself in the case of reaching maximum battery range and/or flying under extreme wind conditions.
  • Auto-generation of vertical waypoints mission: the CopterSonde is able to automatically create and execute a vertical flight wherever it is placed for take-off at the flick of a switch. This feature eliminates the need to manually create the waypoint mission through the ground station, thus mitigating mistakes from the operators and saving time in the deployment.
  • Wind vane flight mode: a simple wind estimation algorithm was developed and implemented on the autopilot. The autopilot estimates the wind direction and adaptively turns the CopterSonde into the wind. By maintaining the CopterSonde orientation into the oncoming wind, the air being drawn across the sensors has not been disturbed by effects from the CopterSonde body. As a result, data contamination is minimized.
  • Customizable shell and payload: the CopterSonde was designed to be a modular system, in particular the payload has its own detachable compartment capable of operating independently to facilitate the calibration and maintenance routines.
  • Smart fan for sensor aspiration: the algorithm toggles the fan’s power on/off at specified heights after takeoff and before landing. This protects the delicate structure of the sensors and from dust and debris.
  • Weather sensor integration: the CopterSonde is able to read a variety of weather sensors that supports I2C or UART protocols. It is currently able to read the bead thermistors distributed by International Met Systems (iMet) and HYT-271 humidity sensors distributed by Innovative Sensor Technology (IST).
  • Custom sensor message for wireless streaming: the autopilot uses the Micro Air Vehicle Link (MAVLink) protocol to code the messages and stream data down to the ground station control. The sensors data can be monitored and processed in real-time while in flight.

Platform Technical Specifications

AIRFRAME PROPULSION SYSTEM
Body Carbon fiber tube (arms)

G10 fiberglass (internal
structure), and aluminum
(connectors and spacers)		 Brushless Electric Motor
Shell 3D printed PLA Lifespan 1600 hrs
Diagonal 50.8 cm kV Rating 700 RMP/V
Height 15.2 cm Maximum Thrust 1.23 km/rotor
Flight Controller Pixhawk Cube Maximum Power 500 W/rotor
T-Style Propellers
Communications Diameter x Pitch 11 x 5.5 in
Telemetry Frequency 915 MHz Material Carbon Fiber
Radio Frequency 2.4 GHz ESC - Motor Speed Controller
Transmission Distance up to 5 km Max. Cont. Current 35 A
Burst Current 45 A
GPS ACCURACY Maximum Voltage 14.8 V (4S LiPo)
Horizontal (RTK) within 3 cm POWER
Horizontal within 1.5 m Battery Type 4S Smart LiPo
Vertical (RTK) within 5 cm Capacity 5870 mAh
Vertical within 3 m Typical Endurance 15 min
Meteorological Specifications Flight Parameters
Thermodynamic Maximum Tilt Angle 40 degrees
Primary variables T, RH, P Maximum Wind Resistance 22 m/s
Derived Variables Td, Tv, θ, θe, θω, r, rs,

q, qs, e, es, LCL,Γ		 Maximum Operating Speed 28 m/s
Accuracy T: within .1 degree C

RH: within 2%

p: within 1.5 hPa		 Maximum Flight Ceiling 6,000 ft AGL
Logging Rate 10-20 Hz Recommended Operating Temperatures -20–40 deg C
Kinematic Typical Ascent Rates 1–5 m/s
Primary variables Tilt angles Typical Descent Rates 1–6 m/s
Derived Variables Horizontal wind speed and direction Weight (sans battery) 1.5 kg
Accuracy Speed: within .6 m/s

Direction: within 4 degrees		 Average All-Up Weight 2 kg
Logging Rate 10-20 Hz For more information regarding the CS or

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