Publications
Found 378 publication(s)
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Silva, B.; Strobl, S.; Bendix, J. & Beck, E. (2016): Canopy evapotranspiration, leaf transpiration and water use efficiency of an Andean pasture in SE-Ecuador – a case study. Erdkunde 70(1), 5-8.
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DOI: 10.3112/erdkunde.2016.01.02
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Abstract:
Abstract:
The relationship between canopy-level evapotranspiration (ETSci) and leaf-level transpiration (Tleaf) as well as photosynthesis (Pleaf) for a homogeneous tropical montane pasture was analyzed over five days using a combination of methods involving a laser scintillometer and a porometer. Weather conditions ranged from overcast to sunny during the period of study. The gas exchange of the leaves of the dominant pasture grass Setaria sphacelata (transpiration vs. photosynthetic CO2 net uptake ) was measured with a porometer and physiologically interpreted on the background of microclimate variables (photosynthetic active radiation (PAR) as proxy for total light intensity, temperature, water vapor deficit of the air) and soil moisture data. Water use efficiency (WUE, photosynthetic CO2 net uptake vs water loss by leaf transpiration) of the pasture was used to analyze the grass’ range of response to the environmental variables of the research area. PAR and water vapor deficit of the air (VPD) appeared to be the determinant factors for Tleaf and ETSci. WUE for the Setaria sphacelata pasture ranged from 1.9 to 5.8 µmol CO2 mmol-1 H20 day-1 and is particularly low during periods of high VPD combined with enhanced insolation during cloudless periods. ET measurements collected by the scintillometer demonstrated a strong correlation with water flux calculated using the Penman-Monteith approach (TPM) (r² = 0.95). Also, Tleaf measured with the porometer showed reasonable coincidence with the ET observations (r² = 0.78). Values of ETSci ranged from 2.26 to 4.96 mm day-1 and Tleaf ranged from 0.83 to 2.41 mm day-1, but only ETSci showed good correspondence with the available energy (net radiation). The lower correlation between Tleaf and canopy-level ETSci compared to that between ETSci and TPM was tested against contaminations from the adjacent fetch area of the scintillometer path, but no effects were found. Likewise, soil water limitations of Tleaf could be ruled out. Therefore, different correlations of ETSci and Tleaf with the incoming energy and VPD may be traced back to a direct effect of the VPD on ET in contrast to its indirect effect on Tleaf which is additionally regulated by physiological processes in the leaf stomata.
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Keywords: |
photosynthesis |
Setaria sphacelata |
scintillometry |
evapotranspiration |
gas-exchange |
scalling |
Wallis, C.I.B.; Paulsch, D.; Zeilinger, J.; Silva, B.; Curatola Fernández, G.F.; Brandl, R.; Farwig, N. & Bendix, J. (2016): Contrasting performance of Lidar and optical texture models in predicting avian diversity in a tropical mountain forest. Remote Sensing of Environment 174, 223-232.
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DOI: 10.1016/j.rse.2015.12.019
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Abstract:
Abstract:
Ecosystems worldwide are threatened by the increasing impact of land use and climate change. To protect their diversity and functionality, spatially explicit monitoring systems are needed. In remote areas, monitoring is difficult and recurrent field surveys are costly. By using Lidar or the more cost-effective and repetitive optical satellite data, remote sensing could provide proxies for habitat structure supporting measures for the conservation of biodiversity. Here we compared the explanatory power of both, airborne Lidar and optical satellite data in modeling the spatial distribution of biodiversity of birds across a complex tropical mountain forest ecosystem in southeastern Ecuador. Weused data fromfield surveys of birds and chose three measures as proxies for different aspects of diversity: (i) Shannon diversity as a measure of ?-diversity that also includes the relative abundance
of species, (ii) phylodiversity as a first proxy for functional diversity, and (iii) community composition as a proxy for combined ?- and ?-diversity.We modeled these diversity estimates using partial least-square regression of Lidar and optical texturemetrics separately and compared themodels using a leave-one-out validated R2 and root mean square error. Bird community information was best predicted by both remote sensing datasets, followed by Shannon diversity and phylodiversity. Our findings reveal a high potential of optical texture metrics for predicting Shannon diversity and a measure of community composition, but not for modeling phylodiversity. Generalizing from the investigated tropical mountain ecosystem,we conclude that texture information retrieved from multispectral data of operational satellite systems could replace costly airborne laser-scanning for modeling certain aspects of biodiversity.
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Keywords: |
Ecuador |
Biodiversity |
Community composition |
Gray level co-occurrence matrix |
Quickbird |
Shannon diversity |
Birds |
Image Texture |
Partial least-square regression |
Phylodiversity |
Carrillo-Rojas, G.; Silva, B.; Cordova, M.; Celleri, R. & Bendix, J. (2016): Dynamic Mapping of Evapotranspiration Using an Energy Balance-Based Model over an Andean Páramo Catchment of Southern Ecuador. Remote Sensing 8(2), 160 (1-24).
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DOI: 10.3390/rs8020160
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Abstract:
Abstract:
Understanding of evapotranspiration (ET) processes over Andean mountain environments is crucial, particularly due to the importance of these regions to deliver water-related ecosystem services. In this context, the detection of spatio-temporal changes in ET remains poorly investigated for specific Andean ecosystems, like the páramo. To overcome this lack of knowledge, we implemented the energy-balance model METRIC with Landsat 7 ETM+ and MODIS-Terra imagery for a páramo catchment. The implementation contemplated adjustments for complex terrain in order to obtain daily, monthly and annual ET maps (between 2013 and 2014). In addition, we compared our results to the global ET product MOD16. Finally, a rigorous validation of the outputs was conducted with residual ET from the water balance. ET retrievals from METRIC (Landsat-based) showed good agreement with the validation-related ET at monthly and annual steps (mean bias error <8 mm·month?1 and annual deviation <17%). However, METRIC (MODIS-based) outputs and the MOD16 product were revealed to be unsuitable for our study due to the low spatial resolution. At last, the plausibility of METRIC to obtain spatial ET retrievals using higher resolution satellite data is demonstrated, which constitutes the first contribution to the understanding of spatially-explicit ET over an alpine catchment in the neo-tropical Andes.
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Keywords: |
Ecuador |
remote sensing |
Andes |
Landsat |
MODIS |
Tropical Mountain Ecosystem |
Paramo |
evapotranspiration |
Tiede, Y.; Homeier, J.; Cumbicus, N.; Peña, J.; Albrecht, J.; Ziegenhagen, B.; Bendix, J.; Brandl, R. & Farwig, N. (2016): Phylogenetic niche conservatism does not explain elevational patterns of species richness, phylodiversity and family age of tree assemblages in Andean rainforest.. Erdkunde 70(1), 83-106.
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DOI: 10.3112/erdkunde.2016.01.06
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Abstract:
Abstract:
Phylogenetic niche conservatism (PNC) is the tendency of species within a clade to retain ancestral traits and
to persist in their primary ecological niches on geological time scales. It links evolutionary and ecological processes and has
been hypothesized to explain patterns of species richness and the composition of species assemblages. Decreasing patterns
of species richness along latitudinal gradients were often explained by the combination of ancient tropical climates, trait
retention of tropical lineages and environmental filtering. PNC also predicts decreasing phylodiversity and family age with
decreasing tropicality and has been invoked to explain these patterns along climatic gradients across latitudinal as well as elevational
gradients. However, recent studies on tree assemblages along latitudinal and elevational gradients in South America
found patterns contradicting the PNC framework. Our study aims to shed light on these contradictions using three different
metrics of the phylogenetic composition that form a gradient from recent evolutionary history to deep phylogenetic
relationships. We analyzed the relationships between elevation and taxonomic species richness, phylodiversity and family
age of tree assemblages in Andean rainforests in Ecuador. In contrast to predictions of the PNC we found no associations
of elevation with species richness of trees and increasing clade level phylodiversity and family age of the tree assemblages
with elevation. Interestingly, we found that patterns of phylodiversity across the studied elevation gradient depended especially
on the deep nodes in the phylogeny. We therefore suggest that the dispersal of evolutionarily old plant lineages with
extra-tropical origins influences the recent composition of tree assemblages in the Andes. Further studies spanning broader
ecological gradients and using better resolved phylogenies to estimate family and species ages are needed to obtain a deeper
mechanistic understanding of the processes that drive the assembly of tree communities along elevational gradients.
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Keywords: |
Andes |
Biodiversity |
Ecudaor |
Bendix, J. & Beck, E. (2016): Environmental change and its impacts in a biodiversity hotspot of the south Eucadorian Andes - monitoring and mitigation strategies . Erdkunde 70(1), 1-4.
Kübler, D.; Günter, S.; Hildebrandt, P.; Stimm, B.; Weber, M.; Mosandl, R.; Muñoz, J.; Aguirre, N.; Cabrera, O.; Zeilinger, J. & Silva, B. (2016): Assessing the importance of topographic variables for the spatial distribution of tree species in a tropical mountain forest.. Erdkunde 70(1), 19-47.
Thies, B.; Nauss, T.; Reudenbach, C.; Cermak, J. & Bendix, J. (2016): Mean Number of Storm Days. In: Mauser, Wolfram, Prasch, Monika (eds.): Regional Assessment of Global Change Impacts ( ), Springer, 271-277.
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Abstract:
Abstract:
Precipitation events are the main driving force for hydrological processes; for this reason, correctly compiling the distribution of precipitation in the study area is given high priority. Therefore, three models for assessing precipitation were implemented in DANUBIA: a mesoscale atmosphere model, an interpolation model based on station data and a satellite-supported rainfall retrieval. The satellite-based derivation of precipitation takes place using data from the European Meteosat system. In a first step, the boundaries of the raining cloud areas are delineated. Second, the precipitation rate is assigned considering the precipitation processes identified before.
Comparing monthly mean precipitation in the study area for 1999 based on the atmospheric model, the interpolation method and the satellite-based technique reveal shortcomings in identifying stratiform precipitation for the satellite method. On the other hand, weather models have slight weaknesses in calculating convective precipitation. Further results show the average number of storm days from May to September between 1995 and 1999 derived using the satellite retrieval technique. The frequency distribution indicates the expected midsummer maximum in July and reveals an increase in thunderstorm frequency caused by orography within the drainage basin.
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Keywords: |
GLOWA-Danube |
DANUBIA |
Storm days |
Upper Danube |
Laffers, W.; Westermann, S.; Regeling, B.; Martin, R.; Thies, B.; Gerstner, A.O.; Bootz, F. & Müller, N.A. (2016): Early recognition of cancerous lesions in the mouth and oropharynx : Automated evaluation of hyperspectral image stacks. HNO 64(1), 27-33.
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DOI: 10.1007/s00106-015-0109-3
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Abstract:
Abstract:
BACKGROUND:
Early detection of cancerous lesions is still crucial for a patient's prognosis. Although diagnostic access to the oral cavity and oropharynx is comparably easy, the incidence of resulting disease remains high. This is due to the fact that in many cases, malignity is recognized too late on a purely visual basis. Previously, we discussed the application of hyperspectral imaging for early detection of precancerous and cancerous lesions of the larynx. This time, we evaluate the method in the oral cavity and oropharynx.
MATERIALS AND METHODS:
In 85 patients scheduled for endoscopy, hyperspectral imaging was performed. We used a rigid 0-degree endoscope, a light-adjustable monochromator, and a hyperspectral camera. For evaluation of the method, 3 patients were chosen exemplarily. Training sites from physiological and cancerous tissues were marked. Hyperspectral data from 1 patient were used to train a classifier, which was then used for automatic detection of precancerous and cancerous lesions in another 2 patients.
RESULTS:
Intraoperative hyperspectral imaging was performed without any problems. Classification showed sensitivities of 61 and 43%, and a specificity of 100%.
CONCLUSION:
This proof-of-concept study underscores the high potential of hyperspectral imaging for early recognition of cancer in the mouth and oropharynx. Besides a better prognosis for cancer patients, this approach could lead to higher cost efficiency in the health system.
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Keywords: |
endoscopy |
Hyperspectral imaging |
Early diagnosis |
Head and neck neoplasms |
oropharyngeal cancer |
Campozano, L.; Celleri, R.; Trachte, K.; Bendix, J. & Samaniego, E. (2016): Rainfall and Cloud Dynamics in the Andes: A Southern Ecuador Case Study. Advances in Meteorology 2016(ID 3192765), 15.
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DOI: 10.1155/2016/3192765
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Abstract:
Abstract:
Mountain regions worldwide present a pronounced spatiotemporal precipitation variability, which added to scarce monitoring
networks limits our understanding of the generation processes involved. To improve our understanding of clouds and precipitation
dynamics and cross-scale generation processes in mountain regions, we analyzed spatiotemporal rainfall patterns using satellite
cloud products (SCP) in the Paute basin (900–4200m a.s.l. and 6481 km2) in the Andes of Ecuador. Precipitation models, using
SCP and GIS data, reveal the spatial extension of three regimes: a three-modal (TM) regime present across the basin, a bimodal
(BM) regime, along sheltered valleys, and a unimodal (UM) regime at windward slopes of the eastern cordillera. Subsequently, the
spatiotemporal analysis using synoptic information shows that the dry season of the BM regime during boreal summer is caused
by strong subsidence inhibiting convective clouds formation.Meanwhile, in UMregions, low advective shallow cap clouds mainly
cause precipitation, influenced by water vapor from the Amazon and enhanced easterlies during boreal summer. TM regions are
transition zones fromUMto BMand zones on the windward slopes of the western cordillera. These results highlight the suitability
of satellite and GIS data-driven statistical models to study spatiotemporal rainfall seasonality and generation processes in complex
terrain, as the Andes.
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Keywords: |
Ecuador |
rainfall |
Yi, L.; Thies, B.; Zhang, S.; Shi, X. & Bendix, J. (2015): Optical Thickness and Effective Radius Retrievals of Low Stratus and Fog from MTSAT Daytime Data as a Prerequisite for Yellow Sea Fog Detection. Remote Sensing 8(1), 8.
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DOI: 10.3390/rs8010008
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Abstract:
Abstract:
Operational nowcasting techniques for sea fog over the Yellow Sea rely on data from weather satellites because ground-based observations are hardly available. While there are several algorithms for detecting low stratus (LST) that are applicable to geostationary weather satellite data, sea fog retrieval is more complicated. These schemes mostly need ancillary data such as Cloud Optical Thickness (COT) and Droplet Effective Radius (DER). To retrieve the necessary parameters for sea fog detection over the Yellow Sea, the Comprehensive Analysis Program for Cloud Optical Measurement (CAPCOM) scheme developed by Kawamoto et al. (2001) was adapted to the Japanese Multifunctional Transport Satellites (MTSAT) system-Japanese Advanced Meteorological Imager (JAMI). COT and DER values were then retrieved for 64 cases over the Yellow Sea (= 85,000 LST pixels) and compared with the COT and DER products from the MYD06/MOD06, CAPCOM-MODIS (Moderate Resolution Imaging Spectroradiometer) and CloudSat (cloud radar). Results showed that the COT and DER values retrieved from JAMI were satisfactory. The MTSAT-2 JAMI data delivered better COT values than the MTSAT-1R JAMI data, due to the re-calibration of MTSAT-2 JAMI’s visible (VIS) band in 2011. Similarly, improvements were seen in DER retrieval, even though the VIS re-calibration primarily affects COT retrieval. By comparing the difference in stratus thickness calculated by MTSAT-1R and MTSAT-2, the COT and DER retrieved from MTSAT-2 JAMI can be used in ground fog retrieval schemes. These values exhibit less bias, especially in cases involving high cloud top and thin cloud thickness. Both the COT and DER retrievals from MTSAT-2 JAMI offer potential as reliable parameters for Yellow Sea fog detection.
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Keywords: |
low stratus |
fog |
MTSAT |
Yellow Sea |
optical thickness |
droplet effective radius |
Rollenbeck, R.; Trachte, K. & Bendix, J. (2015): A new class of quality controls for micrometeorological data in complex tropical environments. J. of Atmos. and Ocean techn.. J. of Atmos. and Ocean techn. Vol 33(No 1), 169-183.
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DOI: 10.1175/JTECH-D-15-0062.1
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Abstract:
Abstract:
Quality control is a particularly demanding problem for micrometeorological studies in complex environments. With the transition to electronic sensing and storage of climate data in high temporal resolution, traditional approaches of homogenization are insufficient for addressing the small-scale variability and spatial heterogeneity of the data. This problem can be successfully addressed by introducing a new class of control procedures based on the physical and climatological relations between different climate variables. The new approach utilizes knowledge about the interdependency of air temperature, precipitation, radiation, relative air humidity, cloud cover and visibility to develop empirical functions for determining the probability margins for the co-occurrence of specific conditions in tropical mountains and deserts. It can also be applied to other geographic settings by adjusting the parameters derived from the data itself. All procedures are integrated into a processing chain with feedback loops and combined with conventional logical and statistical checks, which enables it to detect small errors that normally pass unnoticed. The algorithms are also adapted to incorporate the short time steps of the original data to retain the potential for detailed process analyses.
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Keywords: |
datawarehouse |
data quality |
Kühnlein, M.; Appelhans, T.; Thies, B. & Nauss, T. (2015): Precipitation estimates from MSG SEVIRI daytime, night-time and twilight data with random forests. Journal of Applied Meteorology and Climatology 53, 2457-2480.
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DOI: 10.1175/JAMC-D-14-0082.1
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Abstract:
Abstract:
A new rainfall retrieval technique for determining rainfall rates in a continuous manner (day, twilight, and night) resulting in a 24-h estimation applicable to midlatitudes is presented. The approach is based on satellite-derived information on cloud-top height, cloud-top temperature, cloud phase, and cloud water path retrieved from Meteosat Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) data and uses the random forests (RF) machine-learning algorithm. The technique is realized in three steps: (i) precipitating cloud areas are identified, (ii) the areas are separated into convective and advective-stratiform precipitating areas, and (iii) rainfall rates are assigned separately to the convective and advective-stratiform precipitating areas. Validation studies were carried out for each individual step as well as for the overall procedure using collocated ground-based radar data. Regarding each individual step, the models for rain area and convective precipitation detection produce good results. Both retrieval steps show a general tendency toward elevated prediction skill during summer months and daytime. The RF models for rainfall-rate assignment exhibit similar performance patterns, yet it is noteworthy how well the model is able to predict rainfall rates during nighttime and twilight. The performance of the overall procedure shows a very promising potential to estimate rainfall rates at high temporal and spatial resolutions in an automated manner. The near-real-time continuous applicability of the technique with acceptable prediction performances at 3–8-hourly intervals is particularly remarkable. This provides a very promising basis for future investigations into precipitation estimation based on machine-learning approaches and MSG SEVIRI data.
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Keywords: |
remote sensing |
precipitation |
rainfall |
Thies, B.; Groos, A.; Schulz, M.; Li, C.; Chang, S. & Bendix, J. (2015): Frequency of low clouds in Taiwan retrieved from MODIS data and its relation to cloud forest occurrence. Remote Sensing 7, 12986-13004.
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DOI: 10.3390/rs71012986
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Abstract:
Abstract:
The relationship between satellite-derived low cloud frequency and the occurrence of tropical montane cloud forest (TMCF) in Taiwan was investigated. From daily MODIS cloud mask products between 2003 and 2012 the low cloud class was extracted and mean low cloud frequency was calculated for Taiwan. This low cloud frequency map was blended with an existing plot-based vegetation classification for Taiwan to analyze the relationship between low cloud frequency and TMCF occurrence. Receiver operating characteristics curves and the area under the ROC curve (AUC) were used to analyze if a relationship exists. No relationship was found for all four TMCF types taken together (AUC = 0.61) and for the dominant TMCF type, Quercus montane evergreen broad-leaved cloud forest (AUC = 0.5). Strong relationships were found for the two spatially-restricted TMCF types, Fagus montane deciduous broad-leaved cloud forest (AUC = 0.91) and Pasania-Elaeocarpus montane evergreen broad-leaved forest (AUC = 0.84), as well as for the second dominant type Chamaecyparis montane mixed cloud forest (AUC = 0.74). The results show that low cloud frequency thresholds might be associated with specific cloud forest types in Taiwan. Further studies should incorporate information about cloud base height, cloud density, and cloud immersion time as well as satellite-based cloud frequency information with a higher temporal resolution. Combination with satellite-based land cover classifications for Taiwan would allow quasi-continuous observation of TMCF changes. Such knowledge would be the precondition for effective protective actions concerning this exceptional but threatened ecosystem.
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Keywords: |
MODIS |
Taiwan |
satellite |
tropical montane cloud forest |
vegetation survey |
Cordova, M.; Carrillo-Rojas, G.; Crespo, P.; Wilcox, B. & Celleri, R. (2015): Evaluation of the Penman-Monteith (FAO 56 PM) Method for Calculating Reference Evapotranspiration Using Limited Data: Application to the Wet Páramo of Southern Ecuador. Mountain Research and Development 35(3), 230-239.
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DOI: 10.1659/MRD-JOURNAL-D-14-0024.1
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Abstract:
Abstract:
Reference evapotranspiration (ETo) is often calculated using the Penman-Monteith (FAO 56 PM; Allen et al 1998) method, which requires data on temperature, relative humidity, wind speed, and solar radiation. But in high-mountain environments, such as the Andean páramo, meteorological monitoring is limited and high-quality data are scarce. Therefore, the FAO 56 PM equation can be applied only through the use of an alternative method suggested by the same authors that substitutes estimates for missing data. This study evaluated whether the FAO 56 PM method for estimating missing data can be effectively used for páramo landscapes in the high Andes of southern Ecuador. Our investigation was based on data from 2 automatic weather stations at elevations of 3780 m and 3979 m. We found that using estimated wind speed data has no major effect on calculated ETo but that if solar radiation data are estimated, ETo calculations may be erroneous by as much as 24%; if relative humidity data are estimated, the error may be as high as 14%; and if all data except temperature are estimated, errors higher than 30% may result. Our study demonstrates the importance of using high-quality meteorological data for calculating ETo in the wet páramo landscapes of southern Ecuador.
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Keywords: |
Ecuador |
Andes |
Tropical Mountain Ecosystem |
mount |
mountainous regions |
reference evapotranspiration |
meteorological data |
limited data |
Penman-Monteith |
Trachte, K.; Bissolli, P.; Kennedy, J.; Parker, D.; Trigo, R. & Barriopedro, D. (2015): Regional climates. Europe and the Middle East [in "State of the Climate in 2014"]. Bulletin of the American Meteorological Society 96(7), S193-200.
Lehnert, L.; Meyer, H. & Bendix, J. (2015-07-01). Hyperspectral Data Analysis in R - The new hsdar package. Presented at useR! Conference, Aalborg, Denmark.
Regeling, B.; Laffers, W.; Gerstner, A.O.; Westermann, S.; Müller, N.A.; Schmidt, K.; Bendix, J. & Thies, B. (2015): Development of an image pre-processor for operational hyperspectral laryngeal cancer detection. J. Biophotonics 9(3), 235-245.
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DOI: 10.1002/jbio.201500151
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Abstract:
Abstract:
Hyperspectral imaging (HSI) is a technology with high
potential in the field of non-invasive detection of cancer.
However, in complex imaging situations like HSI of the
larynx with a rigid endoscope, various image interferences
can disable a proper classification of cancerous tissue. We
identified three main problems: i) misregistration of single
images in a HS cube due to patient heartbeat ii) image
noise and iii) specular reflections (SR). Consequently, an
image pre-processor is developed in the current paper to
overcome these image interferences. It encompasses i)
image registration ii) noise removal by minimum noise
fraction (MNF) transformation and iii) a novel SR detection method. The results reveal that the pre-processor improves classification performance, while the newly developed SR detection method outperforms global thresholding technique hitherto used by 46%. The novel pre-processor will be used for future studies towards the development of an operational scheme for HS-based larynx cancer detection.
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Keywords: |
endoscopy |
Hyperspectral imaging |
specular reflection detection |
in-vivo |
larynx |
image processing |
Lehnert, L.; Meyer, H.; Wang, Y.; Miehe, G.; Thies, B.; Reudenbach, C. & Bendix, J. (2015): Retrieval of grassland plant coverage on the Tibetan Plateau based on a multi-scale, multi-sensor and multi-method approach. Remote Sensing of Environment 164, 197-207.
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DOI: 10.1016/j.rse.2015.04.020
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Abstract:
Abstract:
Plant coverage is a basic indicator of the biomass production in ecosystems. On the Tibetan Plateau, the biomass
of grasslands provides major ecosystem services with regard to the predominant transhumance economy. The
pastures, however, are threatened by progressive degradation, resulting in a substantial reduction in plant
coverage with currently unknown consequences for the hydrological/climate regulation function of the plateau
and the major river systems of SE Asia that depend on it and provide water for the adjacent lowlands. Thus,
monitoring of changes in plant coverage is of utmost importance, but no reliable tools have been available to
date to monitor the changes on the entire plateau. Due to the wide extent and remoteness of the Tibetan Plateau,
remote sensing is the only tool that can recurrently provide area-wide data for monitoring purposes. In this
study, we develop and present a grassland-cover product based on multi-sensor satellite data that is applicable
for monitoring at three spatial resolutions (WorldView type at 2–5 m, Landsat type at 30 m, MODIS at 500 m),
where the data of the latter resolution cover the entire plateau. Four different retrieval techniques to derive
plant coverage from satellite data in boreal summer (JJA) were tested. The underlying statistical models are
derived with the help of field observations of the cover at 640 plots and 14 locations, considering the main
grassland vegetation types of the Tibetan Plateau. To provide a product for the entire Tibetan Plateau, plant
coverage estimates derived by means of the higher-resolution data were upscaled to MODIS composites acquired
between 2011 and 2013. An accuracy assessment of the retrieval methods revealed best results for the retrieval
using support vector machine regressions (RMSE: 9.97%, 7.13% and 5.51% from the WorldView to the MODIS
scale). The retrieved values coincide well with published coverage data on the different grassland vegetation
types.
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Keywords: |
MODIS |
Tibetan Plateau |
Partial least square regression |
Plant coverage |
Degradation monitoring |
SVM regression |
Linear spectral unmixing |
Spectral angle mapper |
Vegetation indices |
Curatola Fernández, G.F.; Obermeier, W.; Gerique, A.; López Sandoval, M.F.; Lehnert, L.; Thies, B. & Bendix, J. (2015): Land Cover Change in the Andes of Southern Ecuador - Patterns and Drivers. Remote Sensing 7(3), 2509-2542.
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DOI: 10.3390/rs70302509
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Abstract:
Abstract:
In the megadiverse tropical mountain forest in the Andes of southern Ecuador, a global biodiversity hotspot, the use of fire to clear land for cattle ranching is leading to the invasion of an aggressive weed, the bracken fern, which is threatening diversity and the provisioning of ecosystem services. To find sustainable land use options adapted to the local situation, a profound knowledge of the long-term spatiotemporal patterns of land cover change and its drivers is necessary, but hitherto lacking. The complex topography and the high cloud frequency make the use of remote sensing in this area a challenge. To deal with these conditions, we pursued specific pre-processing steps before classifying five Landsat scenes from 1975 to 2001. Then, we quantified land cover changes and habitat fragmentation, and we investigated landscape changes in relation to key spatial elements (altitude, slope, and distance from roads). Good classification results were obtained with overall accuracies ranging from 94.5% to 98.5% and Kappa statistics between 0.75 and 0.98. Forest was strongly fragmented due to the rapid expansion of the arable frontier and the even more rapid invasion by bracken. Unexpectedly, more bracken-infested areas were converted to pastures than vice versa, a practice that could alleviate pressure on forests if promoted. Road proximity was the most important spatial element determining forest loss, while for bracken the altitudinal range conditioned the degree of invasion in deforested areas. The annual deforestation rate changed notably between periods: ~1.5% from 1975 to 1987, ~0.8% from 1987 to 2000, and finally a very high rate of ~7.5% between 2000 and 2001. We explained these inconstant rates through some specific interrelated local and national political and socioeconomic drivers, namely land use policies, credit and tenure incentives, demography, and in particular, a severe national economic and bank crisis.
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Keywords: |
Ecuador |
land cover change |
remote sensing |
Andes |
fragmentation |
bracken fern |
deforestation drivers |
Landsat |
image pre-processing |
attractors of landscape change |
Rollenbeck, R.; Bayer, F.; Münchow, J.; Rodriguez, R. & Atarama, n. (2015): Climatic cycles and gradients of the El Niño core region in North Peru. Advances in Meteorology vol 2105(1), 1-10.
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DOI: 10.1155/2015/750181
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Abstract:
Abstract:
Climatic processes in northern Peru are evaluated on surface observation independent of modelling studies. The region is characterized by regular oscillations, but episodic El Niño-events introduce strong disturbances. Conceptual models based on observations, remote sensing data, and output of regional climate models are compared with data from a new station network. The results show regular oscillations of all climate variables on the annual and daily time scale. The daily cycle is probably associated with thermotidal forcings, causing gravity waves to emanate from the Andes Cordillera. Main factors are the interaction of large scale pressure systems like the Southeast Pacific High and the intertropical convergence zone (ITCZ). Also, there are regional factors: an extended sea-breeze system, the barrier-effect of the Andes, additional energy input by elevated radiation absorption at the mountain slopes, local wind systems, and the variations of the sea surface temperature. At the coast, a low-level jet works as a thermodynamic energy sink, suppressing deep convection and supporting the aridity. Those patterns are found in most of the station data and the processes of this climate can generally be confirmed. The overturning of this stable system with the onset of El Niño-conditions is possibly caused by disruptions of the regional circulation.
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Keywords: |
radiative transfer |
regional atmospheric circulation |
Weather cycles |
tropisches Südamerika |
Desert |