2017-2018 Türkiye Kar Sezonu İçin MODIS Etkili Kar Örtüsü Ürününün Sentinel 2 Görüntüleriyle Doğrulaması

Abstract

Bu çalışmanın ana amacı Orta Çözünürlüklü Görüntüleme Spektroradyometresi (Moderate Resolution Imaging Spectroradiometer - MODIS)’ne ait etkili kar kaplı alan (EKKA) ürününün Türkiye üzerinde sürekli doğrulama çalışmalarının yapılabilmesi amacıyla Sentinel 2 uydu görüntülerinin uygunluğunun değerlendirilmesidir. Çalışmanın ilk aşamasında, üç farklı ikili kar haritalama algoritması uygulanarak elde edilen Sentinel 2 ikili kar örtüsü haritaları, yer istasyonlarından elde edilen kar derinliği ölçümleri ile test edilmiştir. Sentinel 2 ikili kar haritalarının performansını değerlendirmek için Kasım 2017 ile Nisan 2018 arasında çekilen 205 Sentinel 2 görüntüsü ile 75 yer gözlem istasyonundan alınan 286 kar derinliği ölçümü kullanılmıştır. Üç farklı ikili kar haritalama algoritmasının, POD ≥ 0,86, FAR ≤ 0,08 ve ACC ≥ 0,82 değerleri ile saha bazlı kar derinliği verileriyle yüksek uyum içinde olduğu tespit edilmiştir. İkinci aşamada, 2017-2018 Türkiye kar sezonuna ait 206 MODIS EKKA görüntüsü, Sentinel 2 ikili kar haritalarından elde edilen referans EKKA haritaları kullanılarak test edilmiştir. Analizlerde kullanılan Sentinel 2 görüntüler, bulutluluk oranı maksimum %30 olacak şekilde seçilmiştir. Genel sonuçlar, MODIS EKKA ürünü olan MOD10A1'in RMSE = 0,13 ve R = 0,88 değerleri ile oldukça iyi bir performans sergilediğini göstermiştir. Ay bazlı performans metrikleri analiz edildiğinde, MOD10A1 ürününün doğruluğunun Nisan ayında düştüğü ve bu davranışın temel olarak erime süresi boyunca yamalı kar örtüsüne bağlandığı gözlenmiştir. Buna ek olarak, MOD10A1'in ormanlık alanlarda daha düşük performans sergilediği, ancak makilik ve karışık tarım arazilerinin hakim olduğu alanlarda doğruluğunun yüksek olduğu bulunmuştur.

Keywords

• Sentinel 2
• MODIS
• fraksiyonel kar örtüsü
• uzaktan algılama
• Türkiye

Validation of MODIS Fractional Snow Cover Product for 2017-2018 Snow Season in Turkey by using Sentinel 2 Imagery

Abstract

This study mainly focuses on investigating the suitability of Sentinel 2 data for the continuous validation efforts of fractional snow cover (FSC) product of Moderate Resolution Imaging Spectroradiometer (MODIS) over Turkey. In the first stage of the study, Sentinel 2 binary snow cover maps obtained by applying three different binary snow mapping algorithms were tested against in-situ snow depth measurements. In total, 205 Sentinel 2 images taken between November 2017 and April 2018, 286 snow depth measurement from 75 ground observation stations were used to assess the performance of Sentinel 2 binary snow maps. All three binary snow mapping algorithms were in good agreement with in-situ snow depth data with POD ≥ 0.86, FAR ≤ 0.08 and ACC ≥ 0.82. In the second stage, 206 MODIS FSC images for the 2017-2018 snow season over Turkey were tested by using reference FSC maps generated from Sentinel 2 binary snow maps. Sentinel 2 images used in the analyzes were selected so that the cloud contamination rate on each scene was maximum 30%. Overall results indicated that MODIS FSC product, namely, MOD10A1 exhibited quite good performance with RMSE = 0.13 and R = 0.88. When the monthly-based performance metrics were analyzed it was observed that the accuracy of MOD10A1 product degraded in April and this behavior was mainly attributed to the patchy snow cover during the melting period. Additionally, MOD10A1 was found to exhibit poorer performance over forested areas, whereas its accuracy was high over areas dominated by savannas and mixed agricultural lands.

Keywords

• Sentinel 2
• MODIS
• fractional snow cover
• remote sensing
• Turkey

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