scholarly journals Microwave Land Emissivity Calculations over the Qinghai-Tibetan Plateau Using FY-3B/MWRI Measurements

2019 ◽  
Vol 11 (19) ◽  
pp. 2206
Author(s):  
Ying Wu ◽  
Bo Qian ◽  
Yansong Bao ◽  
George P. Petropoulos ◽  
Xulin Liu ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Tibetan Plateau ◽  
Microwave Radiation ◽  
Land Surface ◽  
Surface Characteristics ◽  
Bare Soil ◽  
Distribution Characteristics ◽  
Atmospheric Conditions ◽  
Surface Emissivity ◽  
Polarization Difference

The Qinghai-Tibetan plateau plays an important role in climate change with its unique characteristics, and the surface emissivity is an important parameter to describe the surface characteristics. It is also very important for the accurate retrieval of surface and atmospheric parameters. Different types of surface features have their own radiation characteristics due to their differences in structure, water content and roughness. In this study, the microwave land surface emissivity (10.65, 18.7, 23.8, 36.5 and 89 GHz) of the Qinghai-Tibetan Plateau was calculated using the simplified microwave radiation transmission equation under clear atmospheric conditions based on Level 1 brightness temperatures from the Microwave Radiation Imager onboard the FY-3B meteorological satellite (FY-3B/MWRI) and the National Centers for Environmental Prediction Final (NCEP-FNL) Global Operational Analysis dataset. Furthermore, according to the IGBP (International Geosphere-Biosphere Program) classified data, the spectrum and spatial distribution characteristics of microwave surface emittance in Qinghai-Tibetan plateau were further analyzed. The results show that almost all 16 types of emissivity from IGBP at dual-polarization (vertical and horizontal) increase with the increase of frequency. The spatial distribution of the retrieving results is in line with the changes of surface cover types on the Qinghai-Tibetan plateau, showing the distribution characteristics of large polarization difference of surface emissivity in the northwest and small polarization difference in the southeast, and diverse vegetation can be clearly seen in the retrieving results. In addition, the emissivity is closely related to the type of land surface. Since the emissivity of vegetation is higher than that of bare soil, the contribution of bare soil increases and the surface emissivity decreases as the density of vegetation decreases. Finally, the source of retrieval error was analyzed. The errors in calculating the surface emissivity might mainly come from spatiotemporal collocation of reanalysis data with satellite measurements, the quality of these auxiliary datasets and cloud and precipitation pixel discrimination scheme. Further quantitative analysis of these errors is required, and even standard procedures may need to be improved as well to improve the accuracy of the calculation.

Developing the soil texture effects on the surface resistance to bare soil based on MOD16 algorithm to estimate evapotranspiration over the Tibetan Plateau

2020 ◽  
Author(s):  
Ling Yuan ◽  
Yaoming Ma ◽  
Xuelong Chen
Keyword(s):  
Tibetan Plateau ◽  
Soil Texture ◽  
Land Surface ◽  
Bare Soil ◽  
The Other ◽  
Accurate Estimation ◽  
Surface Model ◽  
The Tibetan Plateau ◽  
The Mean ◽  
Modified Algorithm

<p>Evapotranspiration (ET), composed of evaporation (ETs) and transpiration (ETc) and intercept water (ETw), plays an indispensable role in the water cycle and energy balance of land surface processes. A more accurate estimation of ET variations is essential for natural hazard monitoring and water resource management. For the cold, arid, and semi-arid regions of the Tibetan Plateau (TP), previous studies often overlooked the decisive role of soil properties in ETs rates. In this paper, an improved algorithm for ETs in bare soil and an optimized parameter for ETc over meadow based on MOD16 model are proposed for the TP. The nonlinear relationship between surface evaporation resistance (r<sub>s</sub><sup>s</sup>) and soil surface hydration state in different soil texture is redefined by ground-based measurements over the TP. Wind speed and vegetation height were integrated to estimate aerodynamic resistance by Yang et al. (2008). The validated value of the mean potential stomatal conductance per unit leaf area (C<sub>L</sub>) is 0.0038m s<sup>-1</sup>. And the algorithm was then compared with the original MOD16 algorithm and a soil water index–based Priestley-Taylor algorithm (SWI–PT). After examining the performance of the three models at 5 grass flux tower sites in different soil texture over the TP, East Asia, and America, the validation results showed that the half-hour estimates from the improved-MOD16 were closer to observations than those of the other models under the all-weather in each site. The average correlation coefficient(R<sup>2</sup>) of the improved-MOD16 model was 0.83, compared with 0.75 in the original MOD16 model and 0.78 in SWI-PT model. The average values of the root mean square error (RMSE) are 35.77W m<sup>-2</sup>, 79.46 W m<sup>-2</sup>, and 73.88W m<sup>-2</sup> respectively. The average values of the mean bias (MB) are -4.08W m<sup>-2</sup>, -52.36W m<sup>-2</sup>, and -11.74 W m<sup>-2</sup> overall sites, respectively. The performance of these algorithms are better achieved on daily (R<sup>2</sup>=0.81, RMSE=17.22W m<sup>-2</sup>, MB=-4.12W m<sup>-2</sup>; R<sup>2</sup>=0.64, RMSE=56.55W m<sup>-2</sup>, MB=-48.74W m<sup>-2</sup>; R2=0.78, RMSE=22.3W m<sup>-2</sup>, MB=-9.82W m<sup>-2</sup>) and monthly (R2=0.93, RMSE=23.35W m<sup>-2</sup>, MB=-2.8W m<sup>-2</sup>; R2=0.86, RMSE=69.11W m<sup>-2</sup>, MB=-39.5W m<sup>-2</sup>; R2=0.79, RMSE=62.8W m<sup>-2</sup>, MB=-9.7W m<sup>-2</sup>) scales. Overall, the results showed that the newly developed MOD16 model captured ET more accurately than the other two models. The comparisons between the modified algorithm and two mainstream methods suggested that the modified algorithm could produce high accuracy ET over the meadow sites and has great potential for land surface model improvements and remote sensing ET promotion for the ET region.</p>

Comparative analysis of land surface parameters on three typical underlying surfaces over the Tibetan Plateau

2020 ◽  
Author(s):  
Zhangwei Ding ◽  
Yaoming Ma ◽  
Xuelong Chen
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Alpine Meadow ◽  
Bare Soil ◽  
Alpine Grassland ◽  
The Tibetan Plateau ◽  
Transfer Coefficients ◽  
Surface Parameters ◽  
Yearly Average ◽  
Land Surface Parameters

<p>To improve land surface parameterizations of radiation and energy balance, eddy covariance measurements were performed on three typical land covers types over the Tibetan Plateau , including bare soil, naturally sparse alpine meadow and dense alpine grassland from 2007 to 2012. We investigated how land surface parameters changed with surface properties and vegetation canopy growth and analyzed the characteristics of diurnal and seasonal variations of aerodynamic parameters. Results show that the annual mean surface albedo and surface roughness lengths for momentum were 0.27 and 2.29 cm, 0.241 and 1.39 cm and 0.19 and 6.52 cm over bare soil, naturally sparse alpine meadow and dense alpine grassland areas, respectively. The yearly average turbulence transfer coefficients for momentum and sensible heat under neutral condition were 4.12×10<sup>-3</sup> and 2.29×10<sup>-3</sup>, 4.11×10<sup>-3</sup> and 2.33×10<sup>-3</sup> and 6.67×10<sup>-3</sup> and 4.14×10<sup>-3</sup>, respectively. The median values of κB<sup>-1</sup> averaged over multiple years are 6.65, 5.89 and 4.88, respectively.</p>

scholarly journals Assessment of the consistency among global microwave land surface emissivity products

2015 ◽  
Vol 8 (3) ◽  
pp. 1197-1205 ◽  
Author(s):  
H. Norouzi ◽  
M. Temimi ◽  
C. Prigent ◽  
J. Turk ◽  
R. Khanbilvardi ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Soil Moisture ◽  
Land Cover ◽  
Land Surface ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Surface Emissivity ◽  
Similar Frequency ◽  
Land Surface Emissivity ◽  
Microwave Imager

Abstract. The goal of this work is to intercompare four global land surface emissivity products over various land-cover conditions to assess their consistency. The intercompared land emissivity products were generated over a 5-year period (2003–2007) using observations from the Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E), the Special Sensor Microwave Imager (SSM/I), the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), and WindSat. First, all products were reprocessed in the same projection and spatial resolution as they were generated from sensors with various configurations. Then, the mean value and standard deviations of monthly emissivity values were calculated for each product to assess the spatial distribution of the consistencies/inconsistencies among the products across the globe. The emissivity products were also compared to soil moisture estimates and a satellite-based vegetation index to assess their sensitivities to changes in land surface conditions. Results show the existence of systematic differences among the products. Also, it was noticed that emissivity values in each product have similar frequency dependency over different land-cover types. Monthly means of emissivity values from AMSR-E in the vertical and horizontal polarizations seem to be systematically lower than the rest of the products across various land-cover conditions which may be attributed to the 01:30/13:30 LT overpass time of the sensor and possibly a residual skin temperature effect in the product. The standard deviation of the analyzed products was lowest (less than 0.01) in rain forest regions for all products and highest at northern latitudes, above 0.04 for AMSR-E and SSM/I and around 0.03 for WindSat. Despite differences in absolute emissivity estimates, all products were similarly sensitive to changes in soil moisture and vegetation. The correlation between the emissivity polarization differences and normalized difference vegetation index (NDVI) values showed similar spatial distribution across the products, with values close to the unit except over densely vegetated and desert areas.

scholarly journals Spatial Distribution of Global Landscape Evaporation in the Early Twenty-First Century by Means of a Generalized Complementary Approach

2020 ◽  
Vol 21 (2) ◽  
pp. 287-298 ◽  
Author(s):  
Wilfried Brutsaert ◽  
Lei Cheng ◽  
Lu Zhang
Keyword(s):  
Spatial Distribution ◽  
Wind Speed ◽  
Land Surface ◽  
Spatial Scales ◽  
Surface Air Temperature ◽  
Aridity Index ◽  
Routine Data ◽  
Net Radiation ◽  
Atmospheric Conditions ◽  
Near Surface

AbstractA generalized implementation of the complementary principle was applied to estimate global land surface evaporation and its spatial distribution. The single parameter in the method was calibrated as a function of aridity index, mainly on the basis of runoff and precipitation data for 524 catchments in different parts of the world. The spatial distribution of annual evaporation from Earth’s land surfaces for 2001–13 was then calculated at a spatial resolution of 0.5°, by means of an available global net radiation dataset (commonly referred to as CERES SYN1deg-Day) and a global forcing dataset (referred to as CRU-NCEP v7) for near-surface temperature, humidity, wind speed, and air pressure. The results are shown to agree with reliable previous estimates by more elaborate methods. The global average evaporation for 2001–13 was found to be 472.65 mm a−1 or 36.96 W m−2. The present method should allow not only future updates but also retroactive historical analyses with routine data of net radiation, near-surface air temperature, humidity, wind speed, and precipitation; its main advantage is that the environmental aridity is deduced from atmospheric conditions and requires no knowledge of surface characteristics, such as soil moisture, vegetation, and terrain, which are highly variable and often difficult to quantify at larger spatial scales. Because they are strictly measurement based, the results can serve also as a reality check for different aspects of climate and related models.

scholarly journals Ground mobile observation system for measuring multisurface microwave emissivity

2021 ◽  
Vol 14 (11) ◽  
pp. 7069-7078
Author(s):  
Wenying He ◽  
Hongbin Chen ◽  
Yuejian Xuan ◽  
Jun Li ◽  
Minzheng Duan ◽  
...  
Keyword(s):  
Land Surface ◽  
Numerical Models ◽  
Bare Soil ◽  
Observation System ◽  
In Situ Observation ◽  
Heterogeneous Distribution ◽  
Polarization Difference ◽  
Microwave Emissivity ◽  
Mobile Observation ◽  
Land Surfaces

Abstract. Large microwave surface emissivities with a highly heterogeneous distribution and the relatively small hydrometeor signal over land make it challenging to use satellite microwave data to retrieve precipitation and to be assimilated into numerical models. To better understand the microwave emissivity over land surfaces, we designed and established a ground observation system for the in situ observation of microwave emissivities over several typical surfaces. The major components of the system include a dual-frequency polarized ground microwave radiometer, a mobile observation platform, and auxiliary sensors to measure the surface temperature and soil temperature and moisture; moreover, observation fields are designed comprising five different land surfaces. Based on the observed data from the mobile system, we preliminarily investigated the variations in the surface microwave emissivity over different land surfaces. The results show that the horizontally polarized emissivity is more sensitive to land surface variability than the vertically polarized emissivity is: the former decreases to 0.75 over cement and increases to 0.90 over sand and bare soil and up to 0.97 over grass. The corresponding emissivity polarization difference is obvious over water (>0.3) and cement (approximately 0.25) but reduces to 0.1 over sand and 0.05 over bare soil and almost 0.01 or close to zero over grass; this trend is similar to that of the Tb polarization difference. At different elevation angles, the horizontally/vertically polarized emissivities over land surfaces obviously increase/slightly decrease with increasing elevation angles but exhibit the opposite trend over water.

scholarly journals Assessment of the consistency among global microwave land surface emissivity products

2014 ◽  
Vol 7 (9) ◽  
pp. 9993-10013 ◽  
Author(s):  
H. Norouzi ◽  
M. Temimi ◽  
C. Prigent ◽  
J. Turk ◽  
R. Khanbilvardi ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Soil Moisture ◽  
Land Cover ◽  
Land Surface ◽  
Weather Prediction ◽  
Surface Boundary ◽  
Surface Emissivity ◽  
Similar Frequency ◽  
Land Surface Emissivity ◽  
Microwave Imager

Abstract. The goal of this work is to inter-compare a number of global land surface emissivity products over various land-cover conditions to assess their consistency. Ultimately, the discrepancies between the studied emissivity products will help interpreting the divergences among numerical weather prediction models in which land emissivity is a key surface boundary parameter. The intercompared retrieved land emissivity products were generated over five-year period (2003–2007) using observations from the Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E), Special Sensor Microwave Imager (SSM/I), The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Windsat. First, all products were reprocessed in the same projection and spatial resolution as they were generated from sensors with various configurations. Then, the mean value and standard deviations of monthly emissivity values were calculated for each product to assess the spatial distribution of the consistencies/inconsistencies among the products across the globe. The emissivity values from four products were also compared to soil moisture estimates and satellite-based vegetation index to assess their sensitivities to the changes in land surface conditions. Results show that systematic differences among products exist and variation of emissivities at each product has similar frequency dependency at any land cover type. Monthly means of emissivity values from AMSR-E in the vertical and horizontal polarizations seem to be systematically lower across various land cover condition which may be attributed to the 1.30 a.m./p.m. overpass time of the sensor and possibly a residual skin temperature effect in the product. The standard deviation of the analysed products was the lowest (less than 0.01) in rain forest regions for all products and the highest in northern latitudes, above 0.04 for AMSR-E and SSM/I and around 0.03 for WindSat. Despite differences in absolute emissivity estimates, all products were similarly sensitive to changes in soil moisture and vegetation. The correlation between the emissivity polarization differences and NDVI values showed similar spatial distribution across the products with values close to the unit except over densely vegetated and desert areas.

scholarly journals Some practical notes on the land surface modeling in the Tibetan Plateau

2009 ◽  
Vol 6 (1) ◽  
pp. 1291-1320 ◽  
Author(s):  
K. Yang ◽  
Y.-Y. Chen ◽  
J. Qin
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Land Surface ◽  
Soil Surface ◽  
Bare Soil ◽  
Heat Fluxes ◽  
The Tibetan Plateau ◽  
Central Plateau ◽  
Alpine Meadows ◽  
Common Land Model

Abstract. The Tibetan Plateau is a key region of land-atmosphere interactions, as it provides an elevated heat source to the middle-troposphere. The Plateau surfaces are typically characterized by alpine meadows and grasslands in the central and eastern part while by alpine deserts in the western part. This study evaluates performance of three state-of-the-art land surface models (LSMs) for the Plateau typical land surfaces. The LSMs of interest are SiB2 (the Simple Biosphere), CoLM (Common Land Model), and Noah. They are run with default parameters at typical alpine meadow sites in the central Plateau and typical alpine desert sites in the western Plateau. The recognized key processes and modeling issues are as follows. First, soil stratification is a typical phenomenon beneath the alpine meadows, with dense roots and soil organic matters within the topsoil, and it controls the profile of soil moisture in the central and eastern Plateau; all models significantly under-estimate the soil moisture within the topsoil. Second, a soil surface resistance controls the surface evaporation from the alpine deserts but it has not been reasonably modeled in LSMs; a new scheme is proposed to determine this resistance from soil water content. Third, an excess resistance controls sensible heat fluxes from dry bare-soil or sparsely vegetated surfaces, and all LSMs significantly under-predict the ground-air temperature difference in the daytime. A parameterization scheme for this resistance has been shown effective to remove this bias.

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