Detecting Rainfall Onset Using Sky Images

Ground-based sky cameras (popularly known as Whole Sky Imagers) are increasingly used now-a-days for continuous monitoring of the atmosphere. These imagers have higher temporal and spatial resolutions compared to conventional satellite images. In this paper, we use ground-based sky cameras to detect the onset of rainfall. These images contain additional information about cloud coverage and movement and are therefore useful for accurate rainfall nowcast. We validate our results using rain gauge measurement recordings and achieve an accuracy of 89% for correct detection of rainfall onset.Comment: Accepted in Proc. TENCON 2016 - 2016 IEEE Region 10 Conferenc

WIDGET: System Performance and GRB Prompt Optical Observations

The WIDeField telescope for Gamma-ray burst Early Timing (WIDGET) is used for a fully automated, ultra-wide-field survey aimed at detecting the prompt optical emission associated with Gamma-ray Bursts (GRBs). WIDGET surveys the HETE-2 and Swift/BAT pointing directions covering a total field of view of 62 degree x 62 degree every 10 secounds using an unfiltered system. This monitoring survey allows exploration of the optical emission before the gamma-ray trigger. The unfiltered magnitude is well converted to the SDSS r' system at a 0.1 mag level. Since 2004, WIDGET has made a total of ten simultaneous and one pre-trigger GRB observations. The efficiency of synchronized observation with HETE-2 is four times better than that of Swift. There has been no bright optical emission similar to that from GRB 080319B. The statistical analysis implies that GRB080319B is a rare event. This paper summarizes the design and operation of the WIDGET system and the simultaneous GRB observations obtained with this instrument.Comment: 19 pages, 11 figures, Accepted to appear in PAS

Use of Aerial Thermal Imaging to Assess Water Status Variability in Hedgerow Olive Orchards

Characterization of the spatial variability in tree water status is a prerequisite to conduct precise irrigation management within an orchard. This study assessed the suitability of a crop water stress index (CWSI) derived from high-resolution aerial thermal imagery to estimate tree water status variability in super high density (SHD) olive orchards. The experiment was conducted at a commercial SHD olive orchard near Seville (southwestern Spain). The drip irrigated trees were submitted to three irrigation regimes (four plots per treatment): a full irrigation treatment replacing the crop water needs (ETc) and two regulated deficit irrigation treatments replacing ca. 45% of ETc. During the irrigation season, meteorological variables, soil moisture content, leaf water potential and leaf gas exchange measurements were performed. Infrared temperature sensors (IRTS) installed about 1 m above the canopies were used to derive the required baselines for CWSI calculation. A thermal camera installed on a mini RPAS (Remote Piloted Aerial System) allowed recording high-resolution thermal images at 5 representative dates of the olive tree growing season. CWSI values derived from aerial thermal imagery were sensitive to the deliberately imposed variations in tree water status within the SHD olive orchard. Maximum stomatal conductance and midday stem water potential showed tight correlations with CWSI. We conclude that high resolution thermal imagery captured from a mini RPAS has proven to be a suitable tool to capture tree water status variability within SHD olive orchards.Ministerio de Economía y Competitividad AGL2012- 34544/ECOLIMAJunta de Andalucía P12-AGR-122

Remotely sensed albedo allows the identification of two ecosystem states along aridity gradients in Africa

Empirical verification of multiple states in drylands is scarce, impeding the design of indicators to anticipate the onset of desertification. Remote sensing‐derived indicators of ecosystem states are gaining new ground due to the possibilities they bring to be applied inexpensively over large areas. Remotely sensed albedo has been often used to monitor drylands due to its close relationship with ecosystem status and climate. Here, we used a space‐for‐time‐substitution approach to evaluate whether albedo (averaged from 2000 to 2016) can identify multiple ecosystem states in African drylands spanning from the Saharan desert to tropical Africa. By using latent class analysis, we found that albedo showed two states (low and high; the cut‐off level was 0.22 at the shortwave band). Potential analysis revealed that albedo exhibited an abrupt and discontinuous increase with increased aridity (1 − [precipitation/potential evapotranspiration]). The two albedo states co‐occurred along aridity values ranging from 0.72 to 0.78, during which vegetation cover exhibited a rapid, continuous decrease from ~90% to ~50%. At aridity values of 0.75, the low albedo state started to exhibit less attraction than the high albedo state. Low albedo areas beyond this aridity value were considered as vulnerable regions where abrupt shifts in albedo may occur if aridity increases, as forecasted by current climate change models. Our findings indicate that remotely sensed albedo can identify two ecosystem states in African drylands. They support the suitability of albedo indices to inform us about discontinuous responses to aridity experienced by drylands, which can be linked to the onset of land degradation.This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDA19030500), the National Key Research and Development Program of China (Grant 2016YFC0503302), the European Research Council (BIODESERT project, ERC Grant Agreement 647038), the Joint PhD, Training Program of the University of Chinese Academy of Sciences, and the Research Foundation of Henan University of Technology (Grant 31401178)

Field experiments to test the use of the normalized-difference vegetation index for phenology detection

Some previous studies have detected the timing of leaf expansion and defoliation using the normalized-difference vegetation index (NDVI), but to examine tree phenology using satellite data, NDVI results should be confirmed using ground-truthing. We examined the relationship between NDVI and tree phenology during leaf expansion and defoliation by simultaneously observing the spectral reflectance of the canopy surface and canopy surface images in a cool-temperate deciduous broad-leaved forest. To define the timing of leaf expansion and defoliation using NDVI, the index should meet three criteria: (1) NDVI should exhibit a monotonous increase or decrease (monotonicity). (2) The relationship between NDVI and the forest canopy\u27s status should be unique (uniqueness). (3) The method is robust against the systematic noise (bias) (robustness). In the spring, NDVI values of 0.2–0.3 (relative values: 0.15–0.28) and 0.6–0.7 (relative values: 0.65–0.78) satisfied all three criteria. NDVI values of 0.6–0.7 can serve as potential criteria for detecting the timing of leaf expansion. In autumn, no NDVI values satisfied all three criteria. Thus, NDVI does not appear to be useful for detecting the timing of defoliation. For an area where evergreen vegetation or snow covers the forest floor in winter, our results suggest that previous uses of NDVI to identify the timing of leaf expansion and defoliation on the basis of the date of the maximum rate of growth or reduction of NDVI and the date with a value midway between the year\u27s maximum and minimum values are misleading

Phenologically-Tuned MODIS NDVI-Based Time Series (2000-2012) For Monitoring Of Vegetation and Climate Change in North-Eastern Punjab, Pakistan

One of the main factors determining the daily variation of the active surface temperature is the state of the vegetation cover It can well be characterized by the Normalized Difference Vegetation Index NDVI The NDVI has the potential ability to signal the vegetation features of different eco-regions and provides valuable information as a remote sensing tool in studying vegetation phenology cycles The vegetation phenology is the expression of the seasonal cycles of plant processes and contributes vital current information on vegetation conditions and their connections to climate change The NDVI is computed using near-infrared and red reflectances and thus has both an accuracy and precision A gapless time series of MODIS NDVI MOD13A1 composite raster data from 18th February 2000 to 16th November 2012 with a spatial resolution of 500 m was utilized Time-series terrestrial parameters derived from NDVI have been extensively applied to global climate change since it analyzes each pixel individually without the setting of thresholds to detect change within a time serie

IR Thermography from UAVs to Monitor Thermal Anomalies in the Envelopes of Traditional Wine Cellars: Field Test

Infrared thermography (IRT) techniques for building inspection are currently becoming increasingly popular as non-destructive methods that provide valuable information about surface temperature (ST) and ST contrast (delta-T). With the advent of unmanned aerial vehicle (UAV)-mounted thermal cameras, IRT technology is now endowed with improved flexibility from an aerial perspective for the study of building envelopes. A case study cellar in Northwest (NW) Spain is used to assess the capability and reliability of low-altitude passive IRT in evaluating a typical semi-buried building. The study comparatively assesses the use of a pole-mounted FLIR B335 camera and a drone-mounted FLIR Vue Pro R camera for this purpose. Both tested IRT systems demonstrate good e ectiveness in detecting thermal anomalies (e.g., thermal bridges, air leakages, constructive singularities, and moisture in the walls of the cellar) but pose some di culties in performing accurate ST measurements under real operating conditions. Working with UAVs gives great flexibility for the inspection, but the angle of view strongly influences the radiometric data captured and must be taken into account to avoid disturbances due to specular reflections.This work was supported by the Spanish Ministry of Science, Innovation and Universities under the National Programme for Research Aimed at the Challenges of Society grant for the project “Bioclimatic Design Strategies in Wine Cellars as Nearly Zero-Energy Building Models” [BIA2014-54291-R]S