Tracking Hummingbirds Using Thermal Moving Velocity Sensor

Tu Xiang Zheng

 

For many years the only way to track wildlife was to simply follow and observe the movement and habits of an animal or to capture an animal and put a tag on it and hope that at sometime in the future that same animal would be recaptured. Today, scientists have new tools to help them to track a wide variety of animals, from butterflies to great white sharks, in order to study how they use their environment, which foods are important and to gain insights into behavior and condition of the creatures as well as to identify key breeding areas that may need protection. 

There are three types of radio tracking systems available today: VHF Radio Tracking, Satellite Tracking and Global Positioning System (GPS) Tracking. But for tracking small animals these technologies are helpless because the transmitters used are so large and heavy. Today, scientists are working on ways to make the tracking devices smaller. Among them are MEMS wireless sensing systems. MEMS technology is enabling the development of inexpensive, autonomous wireless sensors with volumes ranging down to cubic mm.  Combination with miniaturized battery technology is making it possible to check even the smallest birds and insects.

In this paper we describe tracking hummingbird using a thermal moving velocity sensor and a thermal wind sensor. As shown in Fig.1, a Bluetooth thermal moving velocity sensor tag is attached to a hummingbird and a smart phone with a thermal wind sensor is hold by an observer. When the hummingbird is flying in the space the plane projection of the hummingbird flying path will display on the screen of the smart phone. The tracking range can reach 100 meters using class 1 smart phone. Technically it's possible to boost the Bluetooth range over 1000 meters, as some vendors suggest.

A thermal moving velocity sensor includes 12 sensing units each consisting of a heater and a thermopile, which are centro-symmetrically arranged on a silicon substrate. Two opposite units are configured as a pair for measuring a moving velocity component in this direction. So the whole sensor can measure 6 different directional velocity components and each two measured adjacent velocity components are 45 degree in angel. The structure of the thermal wind sensor is similar to the thermal moving velocity sensor. An only difference is that the sensing unit number of the thermal wind sensor is 4 instead of 6. The thermal wind sensor can measure 4 different wind components respectively in x and y directions. The measured data by the thermal moving velocity sensor and thermal wind sensor are collected and processed by the smart phone.

 

Reference to Fig. 2, it is more detail to explain the working principle of tracking hummingbird using the thermal moving velocity sensor and thermal wind sensor. As can be seen, a moving plane coordinate system is set on the hummingbird with a thermal moving velocity sensor and a reference plane coordinate system is set on the ground with a thermal wind sensor and a smart phone.

For the thermal moving velocity sensor the following equations can be formed according to basic trigonometric formulas:

V_yh = u + ν cos α,                                            (1)

V_45degree = u cos 45⁰ + (v cos α) cos 45⁰,         (2)

V _xh  = ν sin α                                                  (3)

 α = arcsin (V_xh /υ)                                           (4)

where u is the velocity of the hummingbird, v is the velocity of the natural wind and α is the incident wind angle, which are relative to the moving plane coordinate system. This is a system of ternary linear equations. The values of the three variables u, v and α can be obtained by substituting the measured values of V_yh, V_45degree  and V_xh and cos 45⁰ = 0.525 into the system, and solving the system.

For the thermal wind sensor, the following equations can be formed according to basic trigonometric formulas:

V_yw = ν cos θ                                                   (5)

V_xw  = ν sin θ                                                  (6)

θ = arctan (V_yw/V_xw)                                       (7)

where v is the velocity of the natural wind and θ is the incident wind angle, which are relative to the ground plane coordinate system.

It should be understood that the measured value of the natural wind velocity in the ground plane coordinate system is the same as the measured value in the moving plane coordinate system. But the wind incident angle is different in the two plane coordinates. This means that the incident angle α in the moving plane coordinate system is replaced by the incident angle θ in the ground plane coordinate system.

According to Cartesian coordinate system conversion, the following equations are available.

y_g = x_h  sin (θ - α) + y_h  cos (θ - α)                  (8)

x_g = x_h  cos (θ - α) + y_h  sin (θ - α)                  (9)

Actually, the moving plane coordinate system can be translated to the ground coordinate system by clockwise rotation of (θ - α) degrees. After translation the data collected by the thermal moving velocity sensor can be used to calculate the velocity, flying path and moving range of the hummingbird, which are relative to the ground plane coordinate system.

This tracking technology can help determine exactly where a hummingbird is at any moment in time and often what that animal is doing. Using the data collected from a thermal moving velocity sensor, scientists can determine the day-to-day movements of a hummingbird, the size of a hummingbird's home range, what other animals share an animal's range and the types of habitats a hummingbird uses. By analyzing all this data, scientists can learn new ways to help control hummingbird populations, determine what impact development might have on a hummingbird population, and determine if there are enough individuals of a particular species in an area to allow for reproduction.