PROBLEM TO BE SOLVED: To suppress affections of reflection of a surrounding scene or the sun, cloud to a roof surface for determining snowfall with accuracy.SOLUTION: When a snowfall state of snow 8 accumulated on a roof (14) is determined using a camera image of a greenhouse roof surface, a range of image processing is restricted to an image processing range 42 corresponding to a position of a greenhouse roof structure member 18, for image processing at an image processing circuit 44. In the processing, the greenhouse roof structure member 18 is colored with a color by which the structure member can be distinguished from the snow 8, for making the structure member a colored structure member 19 or a light emitter 50 can be arranged on the greenhouse roof structure member 18. In addition, when it is detected that there is snowfall by the above-mentioned snowfall detection method, snow melting is started, and when it is detected that there is no snowfall, the snow melting is finished.SELECTED DRAWING: Figure 2COPYRIGHT: (C)2019,JPO&INPIT【課題】屋根面への周囲の景色や太陽・雲の映り込みの影響を抑制させて、高精度の積雪判定を行う。【解決手段】温室屋根面のカメラ画像を使用して屋根（１４）に堆積している雪８の積雪状態を判別する際に、画像処理の範囲を温室屋根構造部材１８の位置に対応する画像処理範囲４２に限定して画像処理回路４４で画像処理を行う。ここで、前記温室屋根構造部材１８を雪８と判別可能な色に着色して着色構造部材１９としたり、前記温室屋根構造部材１８に発光体５０を配設したりすることができる。更に、前記の積雪検知方法で積雪有りを検知したときに融雪を開始し、積雪無しを検知したときに融雪を終了することができる。【選択図】図２
