### Trade-Offs of Drone Operations  
In trace detection of chemical using hyperspectral sensors one of the major challenges is to determine the suitable parameter for the vehicle and the sensor, as shown in Figure 1. The goal of the developed technique is to identify the minimum size of the chemical without increasing the cost of capturing time, and image processing time excessively. To find the suitable minimum mapping size of the chemical, the system operator can select parameters like altitude, image overlap and speed of the vehicle. Other sensor parameters like focal length, spatial resolution, exposure time, and acquisition rate can be selected. The number of images required to cover the area of interest depends on all the parameters mentioned before. The influence of the image overlap is managed by the number of images per second, and it is determined using altitude and sensor configuration as shown in Equation (1).  
\[\text{O}\text{forward}=(1-(\text{D}\text{forward})/\text{H}\text{w})^{*}100 \tag{1}\]  
where Oforward is the forward overlap in percent, Dforward is the distance between exposure stations (m), f is the focal length (mm), H is the distance from the camera projection center to the ground (m), and w is the width of the sensor (mm) [17].  
The spatial resolution on the ground or ground sample distance (GSD) can be calculated using Equation (2),  
\[\text{GSD}=(\text{p}/\text{f})^{*}\text{H} \tag{2}\]  
where GSD is the ground sample distance (cm), p is the size of a pixel (mm) on the sensor, f is the focal length (mm), H is the distance from the camera projection center to the ground (cm).  
Figure 1: Different parameters in drone flights. The outer box represents the target variables, while the inner box shows the parameters that can be directly influenced by the mission planner and derivatives of those parameters.  
One of the important examples of trade-off is geometric tradeoff between altitude of the sensor and area covered during the scanning period, this is dependent on the field of view of the sensor and determines the acquisition time of the raw images. If we increase the altitude it would result in less images for the area of interest, and hence, less processing time, but increasing the altitude has direct impact on the GSD and trace detection in the imagery. On the other hand, lower altitude would lead to higher number of raw images which increases the cost of data processing but gives finer spatial resolution, which increases the probability of trace detection with increase in accuracy [18]. These tradeoffs can be used to balance the accuracy and efficiency of the hyperspectral imaging system. Even though these tradeoffs are obvious in nature, there is a lack of research and publications that explore these parameters, in order to design the system for trace detection of chemical.  
This paper focuses on determining the minimum mapping size of chemicals for trace detection of chemicals used in explosives based on the constraint of altitude of the sensor. The results of the experiments performed in this next section would indicate that altitude of the sensor and minimum mapping size of chemical, which has a significant effect on accuracy when both the variables were changed by relatively large amounts. The results obtained from the experiments leave the user with a flexible range of altitude and MMS that are appropriate for different applications.