تعیین ارتفاع بهینه برای دستیابی به درصد پوشش گیاهی با استفاده از کوادکوپتر (مطالعۀ موردی: منطقۀ رضوانشهر استان یزد)

یکی از ملزومات مطالعات اکوسیستم‌ها، تهیۀ نقشۀ پوشش گیاهی منطقه است. تهیۀ این نقشه، معمولاً مستلزم مطالعۀ میدانی است. ازآنجاکه مطالعات میدانی با صرف هزینه و زمان زیادی همراه است، استفاده از دانش سنجش از دور، یکی از راهکارهای موثر در این زمینه است. در این مطالعه، اقدام به بررسی قابلیت استفاده از عکس‌برداری توسط کوادکوپتر، برای تهیۀ نقشۀ درصد پوشش گیاهی منطقه شده است. در همین راستا، عکس‌برداری از پوشش گیاهی در 9 ارتفاع مختلف از سطح زمین صورت گرفت. پرندۀ مورد استفادۀ این تحقیق، فانتوم 4 مجهز به دوربین با کیفیت 12 مگا‌پیکسل است. ارتفاع عکس‌‌برداری از 20 متری از سطح زمین شروع شده و با توجه به قدرت پوشش پرنده، تا 100 متری به فواصل هر ده متر صورت گرفته است. با افزایش ارتفاع عکس‌برداری، مساحت کل عکس‌برداری‌شده بیشتر شده ولی تفکیک جزئیات کمتر شده و در ارتفاعات پایین، مساحت کل نشان‌داده‌شده کمتر، اما قدرت تفکیک جزئیات بالاتر است. ازآنجاکه با افزایش ارتفاع، دامنۀ دید و ابعاد پلات عکس‌برداری وسیع‌تر می‌شود، اقدام به مقایسۀ آن با مقادیر درصد پوشش گیاهی به‌دست‌آمده از تصاویر گوگل‌ارث گردید که دارای همبستگی 99 درصد بود. همچنین ارتفاع بهینۀ عکس‌برداری برای استخراج درصد پوشش گیاهی تعیین شد. نتایج این تحقیق نشان داد ارتفاع بهینه برای عکس‌برداری جهت محاسبۀ درصد پوشش گیاهی با توجه به تیپ گیاهی موجود در منطقه که درختچه‌ای و به‌طور عمده تاغ است، ارتفاع 90‌ متری است.

identifying the optimal height to be used for calculating vegetation percentage using a quadcopter: a case study of rezvanshahr region, yazd province, iran

introductionremote sensing science has been increasingly used throughout recent years in natural resources studies, especially for assessing and preparing vegetation maps. moreover, aerial photography is widely used as a remote sensing tool, especially the ones taken by quadcopters in inaccessible areas, which could be effective, useful, and innovative. on the other hand, digital observation of the earth is an observed data-based approach in which photos are used to study natural resources. in many cases, using photos in time-specific and comparative studies is highly effective, taking into account the largeness of the area, inaccessibility, and lack of roads. therefore, this study used a quadcopter to take photos from various points at different altitudes and compared them with aerial images to determine which type of photo from which height provides the best information concerning the investigated land and vegetation. therefore, the purpose of this study is to investigate the possibility of using a quadcopter in preparing a vegetation percentage map. materials and methods considering the costly and time-consuming nature of ground sampling of vegetation, this study used vegetation photography, digitizing and analyzing the collected photos after transferring them into computer systems. to this end, first, the intended photography centers were selected in the study area at different altitudes, from 10 meters high to 100 meters. then, a quadcopter was sent to the area, taking photos from each selected center. in this regard, in a single center selected as the indicator within a kilometer radius of the study area, the required images were taken at each altitude class from four main directions, moving from the 100-meter height class to the ten-meter height one. the images were used to calibrate the collected photos and the numerical values of the calculated vegetation percentage. then, the intended maps were extracted based on image dimensions and the coordinates of the selected points in google earth. finally, the phases passed for the photos taken by the quadcopter were repeated for photos obtained from the maps so that vegetation percentage could be calculated based on the prepared maps. results the analysis of the study’s results suggested that the variations of vegetation percentage occurred at a slower pace in the western direction at 90 meters height and above, indicating that the height is the best altitude for determining the region’s vegetation percentage. however, a direct relationship was found between elevation and the changes in vegetation percentage in the eastern and northern directions at 90 meters height and above, with the vegetation percentage remaining unchanged with an increase in elevation. in other words, from 90 meters height beyond, the elevation exerts no influence on the calculated vegetation percentage, making it optimal for photography.as for the southern direction, the vegetation variations remain unchanged from 40 meters height beyond, with the increase in elevation not affecting the calculated vegetation percentage. on the other hand, an extremely high correlation (99%) was found between the data collected in the western direction, indicating a very close relationship between the vegetation percentage values collected from different altitudes by the quadcopter and google earth.in the eastern direction, the first flight level lies at 20 meters high. probably, due to the low density of the vegetation, the larger size of the shrubs, and the small surface shown in the images, the vegetation percentage is considerably different from other points, thus making it unreliable.