The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Sibo Duan - One of the best experts on this subject based on the ideXlab platform.
-
generation of a Time consistent land surface temperature product from modis data
Remote Sensing of Environment, 2014Co-Authors: Sibo Duan, Bohui Tang, Ronglin TangAbstract:Land surface temperature (LST) is crucial for a wide variety of land-atmosphere studies. A long-term and Time-consistent LST product is highly desirable for use in global climate studies. In this study, we developed a method to normalize the Terra-MODIS LST during dayTime to a consistent local Solar Time to generate a Time-consistent LST product. A multiple linear regression model for the slope of LST versus the local Solar Time during the period 10:00-12:00 as a function of the normalized-difference vegetation index, Solar zenith angle, and digital elevation model was established using MSG-SEVIRI data. The regression equation was then applied to normalize the Terra-MODIS LST during dayTime to a consistent local Solar Time (i.e., 11:00 local Solar Time). The accuracy of the proposed method was evaluated using MSG-SEVIRI-derived LST data. The results indicate that the root mean square error of the differences between the LST before temporal normalization and the actual LST (derived from MSG-SEVIRI data) is approximately 1.5 K, whereas those between the LST after temporal normalization and the actual LST is approximately 0.5 K. (C) 2013 Elsevier Inc. All rights reserved.
-
evaluation of six land surface diurnal temperature cycle models using clear sky in situ and satellite data
Remote Sensing of Environment, 2012Co-Authors: Sibo Duan, Ning Wang, Bohui TangAbstract:Land surface temperature (LST) and its diurnal variation are vital to the study of land-atmosphere interactions and climate change. In this study, in situ and MSG-SEVIRI-derived LSTs were used to evaluate the performance of six published diurnal temperature cycle (DTC) models, i.e. the GOT01, GOT01_0, VAN06, JNG06, INA08, and GOT09 models. Two Time intervals were considered: one is the entire day (sunrise to sunrise: Period A), and the other is from 09:00 A.M. to 03:00 A.M. on the following day (local Solar Time) (Period B). The results of Period A indicated that the JNG06 and GOT09 models performed best with overall root mean square errors (RMSEs) of 0.5 K. The GOT01, VAN06, and INA08 models performed similarly with overall RMSEs of 0.8 K. The GOT01_0 model performed the worst with an overall RMSE of 1 K. The results of Period B demonstrated that, except for the GOT01_0 model, the other models produced similar results with overall RMSEs of 0.4 K. However, if the width over the half-period of the cosine term (omega) in the GOT01_0, GOT01, and INA08 models was treated as a free parameter in the model fit during Period A. the performance of the GOT01 and INA08 models was significantly improved and attained the same level of accuracy as the JNG06 and GOT09 models. Although the accuracy of the GOT01_0 model was also improved to an overall RMSE of 0.8 K, with five free parameters, this model cannot accurately describe the variations of the LSTs around sunrise and noon. (c) 2012 Elsevier Inc. All rights reserved.
-
evaluation of six land surface diurnal temperature cycle models using clear sky in situ and satellite data
Remote Sensing of Environment, 2012Co-Authors: Sibo Duan, Ning Wang, Zhaoliang Li, Hua Wu, Bohui TangAbstract:Land surface temperature (LST) and its diurnal variation are vital to the study of land-atmosphere interactions and climate change. In this study, in situ and MSG-SEVIRI-derived LSTs were used to evaluate the performance of six published diurnal temperature cycle (DTC) models, i.e. the GOT01, GOT01_0, VAN06, JNG06, INA08, and GOT09 models. Two Time intervals were considered: one is the entire day (sunrise to sunrise: Period A), and the other is from 09:00 A.M. to 03:00 A.M. on the following day (local Solar Time) (Period B). The results of Period A indicated that the JNG06 and GOT09 models performed best with overall root mean square errors (RMSEs) of 0.5 K. The GOT01, VAN06, and INA08 models performed similarly with overall RMSEs of 0.8 K. The GOT01_0 model performed the worst with an overall RMSE of 1 K. The results of Period B demonstrated that, except for the GOT01_0 model, the other models produced similar results with overall RMSEs of 0.4 K. However, if the width over the half-period of the cosine term (omega) in the GOT01_0, GOT01, and INA08 models was treated as a free parameter in the model fit during Period A. the performance of the GOT01 and INA08 models was significantly improved and attained the same level of accuracy as the JNG06 and GOT09 models. Although the accuracy of the GOT01_0 model was also improved to an overall RMSE of 0.8 K, with five free parameters, this model cannot accurately describe the variations of the LSTs around sunrise and noon. (c) 2012 Elsevier Inc. All rights reserved.
Bohui Tang - One of the best experts on this subject based on the ideXlab platform.
-
influence of temperature inertia on thermal radiation directionality modeling based on geometric optical model
IEEE Transactions on Geoscience and Remote Sensing, 2020Co-Authors: Xiangyang Liu, Bohui Tang, Bohui Tang, Mads Olander RasmussenAbstract:Different from bidirectional reflectance, temperature variation takes some Time with the change of illumination. However, previous thermal radiation directionality (TRD) models have less considered the influence of this temperature inertia (TI) effect. By using the concept of conversion component, this article proposed an improved geometric optical (GO) model, called MGP_TI model. This model considers the TI effect by further dividing the background component into the continuously sunlit, continuously shaded, converted from sunlit to shaded, and converted from shaded to sunlit backgrounds. Upon combining with in situ measurements and a comprehensive simulated data set of component temperatures and prescribing three levels of TI and six observation Times, the TI influence on TRD modeling was comprehensively analyzed. Results indicated that: 1) the overall absolute and relative greatest influence were 0.34 °C and 6.9%, respectively, suggesting that the TI influence on the value of TRD was less significant compared with the land surface temperature (LST) retrieval accuracy and the TRD extent; 2) the TI would weaken TRD on the direction of sun motion, whereas it enhanced the TRD on the opposition direction, and the primary influence was enhancing first and then weakening during the period from 10:30 to 15:30, which were determined by the differences in conversion component fractions; and 3) the TI effect could also result in the delay of the hotspot, and the occurrence and degree of the delay were influenced by the TI strength, local Solar Time and temperature differences of sunlit/shaded components.
-
generation of a Time consistent land surface temperature product from modis data
Remote Sensing of Environment, 2014Co-Authors: Sibo Duan, Bohui Tang, Ronglin TangAbstract:Land surface temperature (LST) is crucial for a wide variety of land-atmosphere studies. A long-term and Time-consistent LST product is highly desirable for use in global climate studies. In this study, we developed a method to normalize the Terra-MODIS LST during dayTime to a consistent local Solar Time to generate a Time-consistent LST product. A multiple linear regression model for the slope of LST versus the local Solar Time during the period 10:00-12:00 as a function of the normalized-difference vegetation index, Solar zenith angle, and digital elevation model was established using MSG-SEVIRI data. The regression equation was then applied to normalize the Terra-MODIS LST during dayTime to a consistent local Solar Time (i.e., 11:00 local Solar Time). The accuracy of the proposed method was evaluated using MSG-SEVIRI-derived LST data. The results indicate that the root mean square error of the differences between the LST before temporal normalization and the actual LST (derived from MSG-SEVIRI data) is approximately 1.5 K, whereas those between the LST after temporal normalization and the actual LST is approximately 0.5 K. (C) 2013 Elsevier Inc. All rights reserved.
-
evaluation of six land surface diurnal temperature cycle models using clear sky in situ and satellite data
Remote Sensing of Environment, 2012Co-Authors: Sibo Duan, Ning Wang, Bohui TangAbstract:Land surface temperature (LST) and its diurnal variation are vital to the study of land-atmosphere interactions and climate change. In this study, in situ and MSG-SEVIRI-derived LSTs were used to evaluate the performance of six published diurnal temperature cycle (DTC) models, i.e. the GOT01, GOT01_0, VAN06, JNG06, INA08, and GOT09 models. Two Time intervals were considered: one is the entire day (sunrise to sunrise: Period A), and the other is from 09:00 A.M. to 03:00 A.M. on the following day (local Solar Time) (Period B). The results of Period A indicated that the JNG06 and GOT09 models performed best with overall root mean square errors (RMSEs) of 0.5 K. The GOT01, VAN06, and INA08 models performed similarly with overall RMSEs of 0.8 K. The GOT01_0 model performed the worst with an overall RMSE of 1 K. The results of Period B demonstrated that, except for the GOT01_0 model, the other models produced similar results with overall RMSEs of 0.4 K. However, if the width over the half-period of the cosine term (omega) in the GOT01_0, GOT01, and INA08 models was treated as a free parameter in the model fit during Period A. the performance of the GOT01 and INA08 models was significantly improved and attained the same level of accuracy as the JNG06 and GOT09 models. Although the accuracy of the GOT01_0 model was also improved to an overall RMSE of 0.8 K, with five free parameters, this model cannot accurately describe the variations of the LSTs around sunrise and noon. (c) 2012 Elsevier Inc. All rights reserved.
-
evaluation of six land surface diurnal temperature cycle models using clear sky in situ and satellite data
Remote Sensing of Environment, 2012Co-Authors: Sibo Duan, Ning Wang, Zhaoliang Li, Hua Wu, Bohui TangAbstract:Land surface temperature (LST) and its diurnal variation are vital to the study of land-atmosphere interactions and climate change. In this study, in situ and MSG-SEVIRI-derived LSTs were used to evaluate the performance of six published diurnal temperature cycle (DTC) models, i.e. the GOT01, GOT01_0, VAN06, JNG06, INA08, and GOT09 models. Two Time intervals were considered: one is the entire day (sunrise to sunrise: Period A), and the other is from 09:00 A.M. to 03:00 A.M. on the following day (local Solar Time) (Period B). The results of Period A indicated that the JNG06 and GOT09 models performed best with overall root mean square errors (RMSEs) of 0.5 K. The GOT01, VAN06, and INA08 models performed similarly with overall RMSEs of 0.8 K. The GOT01_0 model performed the worst with an overall RMSE of 1 K. The results of Period B demonstrated that, except for the GOT01_0 model, the other models produced similar results with overall RMSEs of 0.4 K. However, if the width over the half-period of the cosine term (omega) in the GOT01_0, GOT01, and INA08 models was treated as a free parameter in the model fit during Period A. the performance of the GOT01 and INA08 models was significantly improved and attained the same level of accuracy as the JNG06 and GOT09 models. Although the accuracy of the GOT01_0 model was also improved to an overall RMSE of 0.8 K, with five free parameters, this model cannot accurately describe the variations of the LSTs around sunrise and noon. (c) 2012 Elsevier Inc. All rights reserved.
E Fereres - One of the best experts on this subject based on the ideXlab platform.
-
mapping crop water stress index in a pinot noir vineyard comparing ground measurements with thermal remote sensing imagery from an unmanned aerial vehicle
Precision Agriculture, 2014Co-Authors: Joaquim Bellvert, Pablo J Zarcotejada, E Fereres, Joan GironaAbstract:Characterizing the spatial variability in water status across vineyards is a prerequisite for precision irrigation. The crop water stress index (CWSI) indicator was used to map the spatial variability in water deficits across an 11-ha ‘Pinot noir’ vineyard. CWSI was determined based on canopy temperatures measured with infrared temperature sensors placed on top of well-watered and water-stressed grapevines in 2009 and 2010. CWSI was correlated with leaf water potential (ΨL) (R 2 = 0.83). This correlation was also tested with results from high resolution airborne thermal imagery. An unmanned aerial vehicle equipped with a thermal camera was flown over the vineyard at 07:30, 09:30, and 12:30 h (Solar Time) on 31 July 2009. At about the same Time, ΨL was measured in 184 grapevines. The image obtained at 07:30 was not useful because it was not possible to separate soil from canopy temperatures. Using the airborne data, the correlation between CWSI and ΨL had an R 2 value of 0.46 at 09:30 h and of 0.71 at 12:30 h, suggesting that the latter was the more favorable Time for obtaining thermal images that were linked with ΨL values. A sensitivity analysis of varying pixel size showed that a 0.3 m pixel was needed for precise CWSI mapping. The CWSI maps thus obtained by airborne thermal imagery were effective in assessing the spatial variability of water stress across the vineyard.
-
almond tree canopy temperature reveals intra crown variability that is water stress dependent
Agricultural and Forest Meteorology, 2012Co-Authors: Victoria Gonzalezdugo, Pablo J Zarcotejada, J A J Berni, Lola Suarez, David A Goldhamer, E FereresAbstract:Abstract Tree water status is often characterized by measuring a few leaves and it is not known to what extent such measurements represent the tree as a whole. We present an assessment of the intra-crown temperature variability and its relationship with water status in two almond cultivars. High-resolution imagery was acquired on 30 June 2009 at 11:30, 14:30, and 16:30 h (Solar Time) with a thermal camera on-board an aircraft over an almond orchard in Kern County, CA, USA. Ten irrigation levels were applied, ensuring a wide variability in water status, and each was replicated eight Times. Stem water potential and stomatal conductance were measured on trees of various irrigation regimes at each flight. Significant variation in canopy temperature was found within each crown, probably reflecting differences in stomatal conductance in different parts of the tree crown. The intra-crown standard deviation of canopy temperature (intra-crown σT c ) increased from fully irrigated trees to intermediate irrigation levels, diminishing afterwards in the most stressed treatments. Mean canopy temperature was well correlated with stomatal conductance and stem water potential ( R 2 above 0.65). In trees that had similar mean canopy temperature, intra-crown σT c correlated well with tree water status. Our results quantified in detail the spatial variability in surface temperatures that exists within almond tree crowns and suggest that the intra-crown temperature variation may be a useful indicator of the onset of tree water stress.
I C F Mullerwodarg - One of the best experts on this subject based on the ideXlab platform.
-
on the global distribution of neutral gases in titan s upper atmosphere and its effect on the thermal structure
Journal of Geophysical Research, 2003Co-Authors: R V Yelle, I C F Mullerwodarg, Michael Mendillo, A D AylwardAbstract:[1] Using a Time-dependent general circulation model of Titan’s thermosphere, we calculate the global distribution of neutral gases by winds and diffusion. Our calculations suggest that Solar driven dynamics effectively redistribute constituents, causing considerable diurnal and seasonal changes in gas abundances. Subsidence causes an accumulation of lighter gases on the nightside, with nightTime CH4 mole fractions at equinox near 1400 km reaching up to 50%. The reverse happens on the dayside, where lighter gases are depleted, giving minimum CH4 mole fractions near 1400 km of around 12%. The vertical transport Time scales are around 5–10% of a Titan day, so these extrema in gas abundances are shifted with respect to local noon and midnight by up to 4 hours Local Solar Time (LST). The strong horizontal variations in gas abundances, combined with the local Time shifts of their extrema, have an important impact on the thermal structure and lead to a shift of the nightTime minimum from local midnight towards early morning hours (0330 LST). This coupling between gas distribution and thermal structure on the nightside occurs via dynamical processes, primarily through changes in adiabatic heating. The redistribution of gases effectively controls, through changes in mean molecular weight, the pressure gradients, which in turn control the horizontal and vertical winds, and thereby adiabatic heating and cooling. On the dayside, changes in Solar EUV absorption due to the redistributed gases occur but are comparatively small. Although it is possible with our calculations to identify important processes, Voyager and ground based observations of Titan are currently not sufficient to constrain the dynamics of Titan’s upper atmosphere, but comparisons with forthcoming Cassini observations are highly anticipated. INDEX TERMS: 6005 Planetology: Comets and Small Bodies: Atmospheres—composition and chemistry; 0355 Atmospheric Composition and Structure: Thermosphere—composition and chemistry; 3210 Mathematical Geophysics: Modeling; 6007 Planetology: Comets and Small Bodies: Atmospheres—structure and dynamics; 6025 Planetology: Comets and Small Bodies: Interactions with Solar wind plasma and fields;
I P Koronaki - One of the best experts on this subject based on the ideXlab platform.
-
interrelations of uv global global diffuse Solar irradiance components and uv global attenuation on air pollution episode days in athens greece
Atmospheric Environment, 2002Co-Authors: P S Koronakis, G K Sfantos, A G Paliatsos, J K Kaldellis, J E Garofalakis, I P KoronakiAbstract:Abstract An investigation of global ultraviolet (GUV), global (G) and diffuse (Gd) Solar intensities, continuously recorded over a period of five years at a station in Athens, Greece, and stored on the basis of hourly Time intervals since 1996, has revealed the following: (a) UV-global irradiation, associated with the 290–395 nm wavelength region, constitutes 4.1% of global Solar. (b) UV-global irradiance ranges from an average minimum of 2.4 W m−2 and 3.1% of global Solar in January to an average maximum of 45 W m−2 and 7.8%, respectively, in June, both considered at 13:00, Solar Time. (c) There exists a good correlation among the two dimensionless irradiance ratios GUV/Gd and Gd/G in the form of an exponential relationship. (d) UV-global monthly irradiation data show evidence of temporal variability in Athens, from 1996 to 2000. (e) Anthropogenic and photochemical atmospheric pollutant agents (O3, CO, SO2, NOx, smoke) causing air pollution episodes seem to affect differently Solar irradiance components. The main results of analysis (measurements within ±2 h from Solar noon) indicate that a buildup of O3 and NOx inside the urban Athens plume during cloudless and windless warm days could cause: (i) UV-global irradiance depletion between 5.4% and 14.4%. (ii) Diffuse Solar irradiance enhancement up to 38.1%. (iii) Global Solar irradiance attenuation ranging up to 6.3%.