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Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands
The African continent is facing one of the driest periods in the past three decades as well as continued deforestation. These disturbances threaten vegetation carbon (C) stocks and highlight the need for improved capabilities of monitoring large-scale aboveground carbon stock dynamics. Here we use a satellite dataset based on vegetation optical depth derived from low-frequency passive microwaves (
Soil and vegetation-atmosphere exchange of NO, NH3, and N2O from field measurements in a semi arid grazed ecosystem in Senegal
The alternating between dry and wet seasons and the consecutive microbial responses to soil water content in semiarid ecosystems has significant consequences on nitrogen exchanges with the atmosphere. Three field campaigns were carried out in a semi arid sahelian rangeland in Dahra (Ferlo, Senegal), two at the beginning of the wet season in July 2012 and July 2013, and the third one in November 20
Snow cover and snow albedo changes in the central Andes of Chile and Argentina from daily MODIS observations (2000–2016)
The variables of snow cover extent (SCE), snow cover duration (SCD), and snow albedo (SAL) are primary factors determining the surface energy balance and hydrological response of the cryosphere, influencing snow pack and glacier mass-balance, melt, and runoff conditions. This study examines spatiotemporal patterns and trends in SCE, SCD, and SAL (2000–2016; 16 years) for central Chilean and Argent
Woody plant cover estimation in drylands from Earth Observation based seasonal metrics
From in situ measured woody cover we develop a phenology driven model to estimate the canopy cover of woody species in the Sahelian drylands at 1km scale. The model estimates the total canopy cover of all woody phanerophytes and the concept is based on the significant difference in phenophases of dryland trees, shrubs and bushes as compared to that of the herbaceous plants. Whereas annual herbaceo
Remote sensing of vegetation dynamics in drylands : Evaluating vegetation optical depth (VOD) using AVHRR NDVI and in situ green biomass data over West African Sahel
Monitoring long-term biomass dynamics in drylands is of great importance for many environmental applications including land degradation and global carbon cycle modeling. Biomass has extensively been estimated based on the normalized difference vegetation index (NDVI) as a measure of the vegetation greenness. The vegetation optical depth (VOD) derived from satellite passive microwave observations i
Assessing woody vegetation trends in Sahelian drylands using MODIS based seasonal metrics
Woody plants play a major role for the resilience of drylands and in peoples' livelihoods. However, due to their scattered distribution, quantifying and monitoring woody cover over space and time is challenging. We develop a phenology driven model and train/validate MODIS (MCD43A4, 500 m) derived metrics with 178 ground observations from Niger, Senegal and Mali to estimate woody cover trends from
Global-scale mapping of changes in ecosystem functioning from earth observation-based trends in total and recurrent vegetation
Aim: To evaluate trend analysis of earth observation (EO) dense time series as a new way of describing and mapping changes in ecosystem functioning at regional to global scales. Spatio-temporal patterns of change covering 1982-2011 are discussed in the context of changes in land use and land cover (LULCC). Location: Global. Methods: This study takes advantage of the different phenological cycles o
Assessment of vegetation trends in drylands from time series of earth observation data
This chapter summarizes approaches to the detection of dryland vegetation change and methods for observing spatio-temporal trends from space. An overview of suitable long-term Earth Observation (EO) based datasets for assessment of global dryland vegetation trends is provided and a status map of contemporary greening and browning trends for global drylands is presented. The vegetation metrics suit
Assessing drivers of vegetation changes in drylands from time series of earth observation data
This chapter summarizes methods of inferring information about drivers of global dryland vegetation changes observed from remote sensing time series data covering from the 1980s until present time. Earth observation (EO) based time series of vegetation metrics, sea surface temperature (SST) (both from the AVHRR (Advanced Very High Resolution Radiometer) series of instruments) and precipitation dat
Using earth observation-based dry season NDVI trends for assessment of changes in tree cover in the Sahel
The co-existence of trees and grasses is a defining feature of savannah ecosystems and landscapes. During recent decades, the combined effect of climate change and increased demographic pressure has led to complex vegetation changes in these ecosystems. A number of recent Earth observation (EO)-based studies reported positive changes in biological productivity in the Sahelian region in relation to
An automated field spectrometer system for studying VIS, NIR and SWIR anisotropy for semi-arid savanna
This paper presents the Dahra field spectrometer system (DAFIS) sited in Senegal, West Africa. DAFIS is a unique system that automatically measures the spectro-directional reflectance properties of a semi-arid savanna in the spectral range of 350-1800. nm, daily from sunrise to sunset. The instrumental setup allows studying surface anisotropy for different phenological phases. First data retrieved
Mapping and Evaluation of NDVI Trends from Synthetic Time Series Obtained by Blending Landsat and MODIS Data around a Coalfield on the Loess Plateau
Evaluating temporal consistency of long-term global NDVI datasets for trend analysis
As a way to understand vegetation changes, trend analysis on NDVI (normalized difference vegetation index) time series data have been widely performed at regional to global scales. However, most long-term NDVI datasets are based upon multiple sensor systems and unsuccessful corrections related to sensor shifts potentially introduce substantial uncertainties and artifacts in the analysis of trends.
Monitoring coal fires in Datong coalfield using multi-source remote sensing data
Numerous coal fires burn underneath the Datong coalfield because of indiscriminate mining. Landsat TM/ETM, unmanned aerial vehicle (UAV), and infrared thermal imager were employed to monitor underground coal fires in the Majiliang mining area. The thermal field distributions of this area in 2000, 2002, 2006, 2007, and 2009 were obtained using Landsat TM/ETM. The changes in the distribution were th
Revisiting the coupling between NDVI trends and cropland changes in the Sahel drylands : A case study in western Niger
The impact of human activities via land use/cover changes on NDVI trends is critical for an improved understanding of satellite-observed changes in vegetation productivity in drylands. The dominance of positive NDVI trends in the Sahel, the so-called re-greening, is sometimes interpreted as a combined effect of an increase in rainfall and cropland expansion or agricultural intensification. Yet, th
Mapping gains and losses in woody vegetation across global tropical drylands
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 densi
A Routing Protocol for LoRA Mesh Networks
A limitation of current LoRa networks is their single-hop nature. This causes difficulties in areas with poor Internet access, such as remote rural areas, or challenging radio environments, for example in metropolitan areas, as the LoRa gateway must be placed at a location with backhaul access to the network server, but must nonetheless be reachable by all end devices. To facilitate these applicatA limitation of current LoRa networks is their single-hop nature. This causes difficulties in areas with poor Internet access, such as remote rural areas, or challenging radio environments, for example in metropolitan areas, as the LoRa gateway must be placed at a location with backhaul access to the network server, but must nonetheless be reachable by all end devices. To facilitate these applicat
Human population growth offsets climate-driven increase in woody vegetation in sub-Saharan Africa
The rapidly growing human population in sub-Saharan Africa generates increasing demand for agricultural land and forest products, which presumably leads to deforestation. Conversely, a greening of African drylands has been reported, but this has been difficult to associate with changes in woody vegetation. There is thus an incomplete understanding of how woody vegetation responds to socio-economic