*Article* **Practical Recommendations for Hyperspectral and Thermal Proximal Disease Sensing in Potato and Leek Fields**

### **Simon Appeltans 1, Angela Guerrero 1, Said Nawar 1, Jan Pieters 2 and Abdul M. Mouazen 1,\***


Received: 26 May 2020; Accepted: 12 June 2020; Published: 15 June 2020

**Abstract:** Thermal and hyperspectral proximal disease sensing are valuable tools towards increasing pesticide use efficiency. However, some practical aspects of the implementation of these sensors remain poorly understood. We studied an optimal measurement setup combining both sensors for disease detection in leek and potato. This was achieved by optimising the signal-to-noise ratio (SNR) based on the height of measurement above the crop canopy, off-zenith camera angle and exposure time (ET) of the sensor. Our results indicated a clear increase in SNR with increasing ET for potato. Taking into account practical constraints, the suggested setup for a hyperspectral sensor in our experiment involves (for both leek and potato) an off-zenith angle of 17◦, height of 30 cm above crop canopy and ET of 1 ms, which differs from the optimal setup of the same sensor for wheat. Artificial light proved important to counteract the effect of cloud cover on hyperspectral measurements. The interference of these lamps with thermal measurements was minimal for a young leek crop but increased in older leek and after long exposure. These results indicate the importance of optimising the setup before measurements, for each type of crop.

**Keywords:** hyperspectral; thermal; proximal sensing; disease detection; signal-to-noise ratio
