قابليت داده‌هاي ماهواره IRS در برآورد تاج پوشش گياهي (مطالعه موردي:چهارمحال و بختياري)

Capability of IRS satellite on vegetation cover estimation (Case Study: Chaharmah-va-Bakhtiari)

پژوهشگران مختلف سنجش از دور در طول دو دهه گذشته نقش شاخص‏هاي گياهي حاصل از داده‏هاي ماهواره‏اي را در بررسي منابع طبيعي ارزيابي كرده و به همبستگي مناسبي ميان اين شاخص‏ها با پارامتر‏هاي گياهي رسيده‏اند. هدف از اين مطالعه بررسي قابليت شاخص‏هاي طيفي ماهوارهIRSبه منظور برآورد تاج پوشش گياهي در مراتع كرسنك مي‏باشد. پيش پردازش‏هاي مختلف، شامل تصحيح هندسي و تصحيحات اتمسفريك با استفاده از نقشه‏هاي توپوگرافي 1:25000 و روش تفريق عارضه تاريك انجام شد عمليات برداشت زميني در خرداد ماه 1389 در سطحي معادل576 هكتار انجام پذيرفت. پس از تيپ‏بندي واحد‏هاي گياهي با روش نمونه برداري سيستماتيك-تصادفي نمونه برداري انجام گرديد. اندازه گيري تاج پوشش به روش تعيين ميزان سطح پوشيده شده توسط گياه به تفكيك گونه و فرم رويشي اندازه‌گيري و موقعيت هر پلات توسطGPS ثبت شد. در اين مطالعه از تصاوير مربوط به خرداد 1389 استفاده شد. شاخص‏هاي گياهي بر روي تصاوير اعمال وبه همراه اطلاعات تاج پوشش گياهي در محل هر پلات وارد نرم‏افزارSPSSگرديد وبا در نظر گرفتن تاج پوشش به عنوان متغير وابسته و شاخص گياهي به عنوان متغير مستقل همبستگي آنها محاسبه وشاخص‏هايي كه بيشترين همبستگي را با تاج پوشش گياهي داشتند، جهت تهيه مدل انتخاب شدند. نتايج نشان داد كه شاخص GNDVIو DVI با تاج پوشش كل و شاخص PD321 با تاج پوشش فورب‏ها و شاخص GNDVI، GI و MIRV2 با تاج پوشش گندميان بيشترين همبستگي را داشته‏اند.

Over the last two decades, many researchers had investigated the efficiency of vegetation indexes which obtained from satellite in evaluation of naturals resources, and reported appropriate correlation between vegetation indexes and vegetation cover parameters. So this study was conducted to evaluate efficiency of spectral indexes of IRS satellite in order to estimate the vegetation cover of Karsank rangelands. Scientists evaluated the role of plant indexes which obtained from satellite date, on natural resources, during the last decades. They achieved to a good correction between plant indexes with plant parameters. The purpose of this study was to evaluate the capability spectral index of IRS for estimating canopy in KARSANAK rangelands. Variety of pre-processing, including geometric correction and atmospheric correction, were performed by topographic maps (1:25000) and dark object subtraction. Data of experimental field were collected from an area about 576 ha in May 2010. The vegetation unit types were determined and sampling was performed by random-systematic method. Canopy cover was measured by determination of the area that was cover by each species and each of the vegetative forms and the position of the plots were recorded by GPS. The images which were taken in May 2010 were applied in this study. Vegetation indexes were applied on satellite images then related information of canopy cover at each plot imported into the SPSS software, then canopy cover were taken as dependent variable and vegetation indexes as independent variable to define the correlation between them, so the vegetation indexes which had higher correlation with canopy cover were selected to do modeling. The results showed that the indexes of GNDVI and DVI had the most correlation with total canopy cover and the index of PD321 showed highest correlation with canopy cover of forbs, also canopy cover of grass had highest correlation with the indexes of GNDVI, GI and MIRV2.