A Comparative Study of Cross-Product NDVI Dynamics in the Kilimanjaro Region—A Matter of Sensor, Degradation Calibration, and Significance

Detsch, Florian; Otte, Insa; Appelhans, Tim; Nauss, Thomas

doi:10.3390/rs8020159

Cited by 26 publications

(19 citation statements)

References 39 publications

(63 reference statements)

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“…Zhang et al [17] also reported that the annual NDVI from Terra C6 showed larger greening vegetation area than Terra C5 at global scale, which was consistent with the result of our study. Besides, in a comparative study of cross-product NDVI dynamics in a tropical region in Tanzania, significant increasing trends in NDVI also became more apparent in Terra C6 NDVI than C5 NDVI [20]. In this study, the regional average GSNDVI C6 was significantly lower than GSNDVI C5 (Figure 1).…”

Section: Discussionmentioning

confidence: 82%

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Uncertainty of Remote Sensing Data in Monitoring Vegetation Phenology: A Comparison of MODIS C5 and C6 Vegetation Index Products on the Tibetan Plateau

Zheng

Zhu

2017

Remote Sensing

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Vegetation phenology is considered a sensitive indicator of climate change, which controls carbon, nitrogen, and water cycles within terrestrial ecosystems. The Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) is an important moderate resolution remote sensing data for monitoring vegetation phenology. However, Terra MODIS Collection 5 (C5) vegetation index products were identified to be affected by sensor degradation, which has been addressed in the recently released MODIS Collection 6 (C6) vegetation index products. In order to compare the difference between MODIS C5 and C6 NDVI in monitoring vegetation phenology, the start and end of growing season (SOS and EOS) of the alpine grassland on the Tibetan Plateau (TP) were extracted using four common methods. Then, the C5 and C6 NDVI-derived SOS (SOS C5 and SOS C6 ) and EOS (EOS C5 and EOS C6 ) were compared with ground-observed phenology data. Results showed that the multi-year average growing season NDVIs of C6 were lower than those of C5 in most areas, while the inter-annual variation patterns of regional average SOS C5 and SOS C6 (EOS C5 and EOS C6 ) were consistent. However, large spatial differences in phenological trends were found between C5 and C6 NDVI products. From C5 to C6, pixels with a SOS (EOS) trend shifting from significant to insignificant or from insignificant to significant accounted for at least 14.58% (9.07%) of the total pixels. SOS C5 was more consistent than SOS C6 with the ground-observed green-up dates. C5 NDVI may be more appropriate for monitoring SOS than C6 NDVI in the study region, but more ground-observed phenology records are needed to confirm it due to only four observational sites in this study. However, large differences and poor correlations existed between EOS C5 (EOS C6 ) and the ground-observed beginning of leaf coloring. To further evaluate the uncertainty of MODIS C5 and C6 NDVI in monitoring vegetation phenology, higher resolution near-surface remote sensing data and corresponding validation methods should be applied.

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Section: Discussionmentioning

confidence: 82%

“…The differences between MODIS C5 and C6 NDVI have been evaluated in some previous studies (e.g., [17,20]). However, no study has conducted a comparative analysis of the performance of MODIS C5 and C6 NDVI in monitoring vegetation phenology.…”

Section: Introductionmentioning

confidence: 99%

Uncertainty of Remote Sensing Data in Monitoring Vegetation Phenology: A Comparison of MODIS C5 and C6 Vegetation Index Products on the Tibetan Plateau

Zheng

Zhu

2017

Remote Sensing

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“…Estimates of NDVI were calculated from a MODIS Aqua product MYD13Q1 with a horizontal resolution of 250 m by 250 m by averaging corrected NDVI measured of 10 consecutive years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) and extracting pixel values corresponding to the geographical positions of the study sites. For details, see Detsch, Otte, Appelhans, and Nauss (2016) and Peters et al (2016Peters et al ( , 2019).…”

Section: Study Sites and Environmental Datamentioning

confidence: 99%

Leaf traits mediate changes in invertebrate herbivory along broad environmental gradients on Mt. Kilimanjaro, Tanzania

Njovu

Peters

Costa

et al. 2019

Journal of Animal Ecology

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Temperature, primary productivity, plant functional traits, and herbivore abundances are considered key predictors of leaf herbivory but their direct and indirect contributions to community‐level herbivory are not well understood along broad climatic gradients. Here, we determined elevational herbivory patterns and used a path analytical approach to disentangle the direct and indirect effects of climate, land use, net primary productivity (NPP), herbivore abundance, and plant functional traits on community‐level invertebrate herbivory along the extensive elevational and land use gradients at Mt. Kilimanjaro, Tanzania. We recorded standing leaf herbivory caused by leaf chewers, leaf miners and leaf gallers on 55 study sites distributed in natural and anthropogenic habitats along a 3,060 m elevation gradient. We related the total community‐level herbivory to climate (temperature and precipitation), NPP, plant functional traits (specific leaf area, leaf carbon‐to‐nitrogen [CN] ratio and leaf nitrogen‐to‐phosphorus [NP] ratio) and herbivore abundances. Leaf herbivory ranged from 5% to 11% along the elevation gradient. Total leaf herbivory showed unimodal pattern in natural habitats but a strongly contrasting bimodal pattern in anthropogenic habitats. We also detected some variation in the patterns of leaf herbivory along environmental gradients across feeding guilds with leaf chewers being responsible for a disproportionally large part of herbivory. Path analyses indicated that the variation in leaf herbivory was mainly driven by changes in leaf CN and NP ratios which were closely linked to changes in NPP in natural habitats. Similarly, patterns of leaf herbivory in anthropogenic habitats were best explained by variation in leaf CN ratios and a negative effect of land use. Our study elucidates the strong role of leaf nutrient stoichiometry and its linkages to climate and NPP for explaining the variation in leaf herbivory along broad climatic gradients. Furthermore, the study suggests that climatic changes and nutrient inputs in the course of land use change may alter leaf herbivory and consequently energy and nutrient fluxes in terrestrial habitats.

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“…We used the Collection 6 Terra MODIS monthly product MOD13C2 with a spatial resolution of 0.05°(about 5.5 km at equator) and covering from 2000 to present (Didan, 2015). The surface reflectance bands have been corrected for atmospheric effects (Vermote & Kotchenova, 2008) and sensor degradation (Lyapustin et al, 2014;Detsch et al, 2016). To match the spatial resolution of VOD data, the red and near-infrared reflectance bands were aggregated to 0.25°by averaging before the calculation of NDVI.…”

Section: Ndvi and Vod Datamentioning

confidence: 99%

Mapping gains and losses in woody vegetation across global tropical drylands

Tian

Brandt

Liu

et al. 2016

Global Change Biology

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Woody vegetation in global tropical drylands is of significant importance for both the interannual variability of the carbon cycle and local livelihoods. Satellite observations over the past decades provide a unique way to assess the vegetation long-term dynamics across biomes worldwide. Yet, the actual changes in the woody vegetation are always hidden by interannual fluctuations of the leaf density, because the most widely used remote sensing data are primarily related to the photosynthetically active vegetation components. Here, we quantify the temporal trends of the nonphotosynthetic woody components (i.e., stems and branches) in global tropical drylands during 2000-2012 using the vegetation optical depth (VOD), retrieved from passive microwave observations. This is achieved by a novel method focusing on the dry season period to minimize the influence of herbaceous vegetation and using MODerate resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data to remove the interannual fluctuations of the woody leaf component. We revealed significant trends (P < 0.05) in the woody component (VOD ) in 35% of the areas characterized by a nonsignificant trend in the leaf component (VOD modeled from NDVI), indicating pronounced gradual growth/decline in woody vegetation not captured by traditional assessments. The method is validated using a unique record of ground measurements from the semiarid Sahel and shows a strong agreement between changes in VOD and changes in ground observed woody cover (r = 0.78). Reliability of the obtained woody component trends is also supported by a review of relevant literatures for eight hot spot regions of change. The proposed approach is expected to contribute to an improved assessment of, for example, changes in dryland carbon pools.

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A Comparative Study of Cross-Product NDVI Dynamics in the Kilimanjaro Region—A Matter of Sensor, Degradation Calibration, and Significance

Cited by 26 publications

References 39 publications

Uncertainty of Remote Sensing Data in Monitoring Vegetation Phenology: A Comparison of MODIS C5 and C6 Vegetation Index Products on the Tibetan Plateau

Uncertainty of Remote Sensing Data in Monitoring Vegetation Phenology: A Comparison of MODIS C5 and C6 Vegetation Index Products on the Tibetan Plateau

Leaf traits mediate changes in invertebrate herbivory along broad environmental gradients on Mt. Kilimanjaro, Tanzania

Mapping gains and losses in woody vegetation across global tropical drylands

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