Thermal infrared remote sensing for high-resolution minimum temperature mapping | Il telerilevamento all'infrarosso termico per la mappatura delle temperature minime ad elevato dettaglio territoriale

Minimum temperature forecast is particularly important for scheduling spring frost protection. The natural variability of minimum night temperature is strongly affected by the physical mechanisms ruling over energetic exchanges between soil and atmosphere. Under stable nocturnal thermal conditions (as in the case of frost nights), temperature differentiation patterns are created, strongly linked to the morphological features of individual areas. A high-resolution survey, like the one obtainable from thermal infrared (TIR) remote sensing, allows a temperature mapping, where differences among sites can be highlighted. In two frost-prone fruit-growing areas (Rotaliana Plain and lower Non Valley) in Trentino, northern Italy, airborne TIR surveys have been undertaken and the relevant thermal maps have been produced at a 10-m resolution. Calibration was carried out by contemporary ground measurements. Since emissivity remarkably changes depending on landcover features, an empirical calibration is proposed, carried out by ground temperature measurements, that enables to distinguish between any parcel, according to land use. The application to the real case led to temperature assessment errors of 0.95°C (as root of mean-squared errors, RMSE). Finally, in order to assess temperature at 2 m from its airborne TIR estimate at the ground level, statistical relationships have been investigated between values measured at the ground and at 2 m at some sample sites within the two target areas. Even if some outcomes are interesting and potentially useful, some inhomogeneity has resulted, partially hampering the general trial of temperature assessment at the conventional height of 2 m. Further investigation might lead to a fine-tuning of the procedures of temperature measurement and assessment. The methodology is proposed for a minimum temperature prediction at a high territorial resolution: a ground temperature pattern could be applied to reproduce the thermal anomaly referred to a site where an independently calibrated forecast is already known.