Assuming the image presented below is captured by a smartphone camera equipped with a $4mm$ lens and a $\frac{1}{2\mathrm{.}5}"$ sensor $(5\mathrm{.}76mm4\mathrm{.}29mm),$ and considering a drone distance of approximately $20m,$ undertake the following tasks:

a$)$ Compute the Field of View $($FOV$),$ base coverage $($both horizontal and vertical$),$ and image scale. Utilizing the obtained results, make an estimate of the drone's height above the take$-$off point $($refer to Figure $1)$

b$)$ Calculate the distance necessary for the drone to achieve equivalent horizontal base coverage $($note that the photo was taken in portrait$)$ when utilising the following cameras:

A Sony Alpha mirrorless camera with an APS$-$C sensor $14\mathrm{.}9mm)$ and a $35mm$ lens;

A Panasonic Lumix camera with a crop factor of $2$ and a $50mm$ lens.

Figure $1.$The red arrow indicates the height of the drone above the take$-$off point $($h$).$