共查询到20条相似文献，搜索用时 33 毫秒
1.
A. K. Varma R. M. Gairola Samir Pokhrel B. S. Gohil A. K. Mathur Vijay K. Agarwal 《Journal of Earth System Science》2002,111(3):257-266
In this paper rain estimation capability of MSMR is explored. MSMR brightness temperature data of six channels corresponding
to three frequencies of 10, 18 and 21 GHz are colocated with the TRMM Microwave Imager (TMI) derived rain rates to find a
new empirical algorithm for rain rate by multiple regression. Multiple correlation analysis involving various combinations
of channels in linear and non-linear forms and rain rate from TMI is carried out, and thus the best possible algorithm for
rain rate measurement was identified which involved V and H polarized brightness temperature measurements at 10 and 18 GHz
channels. This algorithm explained about 82 per cent correlation (r) with rain rate, and 1.61 mm h-1 of error of estimation.
Further, this algorithm is used for generating global average rain rate map for two contrasting months of August (2000) and
January (2001) of northern and southern hemispheric summers, respectively. MSMR derived monthly averaged rain rates are compared
with similar estimates from TRMM Precipitation Radar (PR), and it was found that MSMR derived rain rates match well, quantitatively
and qualitatively, with that from PR. 相似文献
2.
The brightness temperatures of the Microwave sensor MSMR (Multichannel Scanning Microwave Radiometer) launched in May 1999
onboard Indian Oceansat-1 IRS-P4 are used to develop a direct retrieval method for latent heat flux by multivariate regression
technique. The MSMR measures the microwave radiances at 8 channels at frequencies of 6.6, 10.7, 18 and 21 GHz at both vertical
and horizontal polarizations. It is found that the surface LHF (Latent Heat Flux) is sensitive to all the channels. The coefficients
were derived using the National Centre for Environmental Prediction (NCEP) reanalysis data of three months: July, September,
November of 1999. The NCEP daily analyzed latent heat fluxes and brightness temperatures observed by MSMR were used to derive
the coefficients. Validity of the derived coefficients was checked within situ observations over the Indian Ocean and with NCEP analyzed LHF for global points. The LHF derived directly from the MSMR brightness
temperature (Tb) yielded an accuracy of 35 watt/m2. LHF was also computed by applying bulk formula using the geophysical parameters extracted from MSMR. In this case the errors
were higher apparently due to the errors involved in derivation of the geophysical parameters. 相似文献
3.
4.
P. N. Mahajan R. M. Khaladkar S. G. Narkhedkar Sathy Nair P. C. Joshi P. K. Pal 《Journal of Earth System Science》2004,113(2):223-233
In this paper, daily variations of satellite-derived geophysical parameters such as integrated water vapour (IWV), cloud liquid
water content (CLW), sea surface temperature (SST) and sea surface wind speed (SSW) have been studied for a case of monsoon
depression that formed over the Bay of Bengal during 19th-24th August 2000. For this purpose, IRS P4 MSMR satellite data have
been utilized over the domain equator — 25‡N and 40‡-100‡E. An integrated approach of satellite data obtained from IRS-P4,
METEOSAT-5 and INSAT was made for getting a signal for the development of monsoon depression over the Indian region. Variations
in deep convective activity obtained through visible, infrared and OLR data at 06 UTC was thoroughly analyzed for the complete
life cycle of monsoon depression. Geophysical parameters obtained through IRS-P4 satellite data were compared with vorticity,
convergence and divergence at 850 and 200 hPa levels generated through cloud motion vectors (CMVs) and water vapour wind vectors
(WVWVs) obtained from METEOSAT-5 satellite. This comparison was made for finding proper consistency of geophysical parameters
with dynamical aspects of major convective activity of the depression.
From the results of this study it is revealed that there was strengthening of sea surface winds to the south of low-pressure
area prior to the formation of depression. This indicated the possibility of increase in cyclonic vorticity in the lower troposphere.
Hence, wind field at 850 hPa with satellite input of CMVs in objective analysis of wind field using optimum interpolation
(OI) scheme was computed. Maximum cyclonic vorticity field at 850 hPa was obtained in the region of depression just one day
before its formation. Similarly, with the same procedure maximum anticyclonic vorticity was observed at 200 hPa with WVWVs
input. Consistent convergence and divergence at 850 and 200 hPa was noticed with respect to these vorticities. In association
with these developments, we could get lowest values of OLR (120 W/m2 ) associated with major convective activity that was consistent with the maximum values of integrated water vapour (6-8gm/cm2) and cloud liquid water content (50-60 mg/cm2 ) persisting particularly in the southwest sector of the monsoon depression. 相似文献
5.
The SSM/I microwave Brightness Temperatures (TB's) in the frequency domains of 85 and 19 GHz gathered from the Defense Meteorological Satellite Program (DMSP)-F8 satellite form the basis of this research. These data are related to 27 map times of 13 typhoons of the 1987 season, one typhoon of the 1988 season and one cyclone in the Indian Ocean in 1987. The TB's disclosed certain characteristics of typhoons unavailable through conventional infrared (IR) imagery means.Brightness Temperatures were chosen to delineate the typhoon characteristics rather than the derived geophysical parameters such as rainfall or surface winds because the TB's have better resolution. The footprint size of the 85 GHz TB is 15 × 13 km while a derived (through algorithms based on regression) quantity such as rainfall has a much higher footprint size. The relatively large footprint size of rainfall results, because of using the 19 GHz channel which has a larger footprint size of 69 × 43 km.The mean 85 GHz (vertically polarized, V) TB's of a moving typhoon, particularly those on the left side within 55 km of the center, appear to exhibit a practically usable correlation with the 24 hour intensity. This finding is consistent with some observational studies, which show higher rain rates to occur within the asymmetric eyewalls of developing tropical cyclones. Further stratification of the sample in terms of direction of movement improved the correlation.The TB anomalies were defined in terms of the TB differences between two sections of a typhoon (e.g., between right and left sides or between inner and outer areas). The development of this sort of anomalies represents a relative growth of deep convection close to the center. If there is a good growth, the cyclone is likely to intensify within a short period of time. The anomalies also showed good correlation with the 24-h intensity. The intensity change (24-h intensity – Current Intensity) was also correlated with the 85 GHz V mean TB values, as well as, with 85 GHz V TB anomalies as defined above. Significant correlations ensued. Since these preliminary results are promising, further experimentation with a larger sample is suggested. Nevertheless, the scientist interested in natural hazards would find the current results valuable in the problem of typhoon intensification. 相似文献
6.
Pravin K. Rana Mihir K. Dash A. Routray P. C. Pandey 《Journal of the Geological Society of India》2011,78(2):99-108
Antarctic sea ice cover plays an important role in shaping the earth’s climate, primarily by insulating the ocean from the
atmosphere and increasing the surface albedo. The convective processes accompanied with the sea ice formation result bottom
water formation. The cold and dense bottom water moves towards the equator along the ocean basins and takes part in the global
thermohaline circulation. Sea ice edge is a potential indicator of climate change. Additionally, fishing and commercial shipping
activities as well as military submarine operations in the polar seas need reliable ice edge information. However, as the
sea ice edge is unstable in time, the temporal validity of the estimated ice edge is often shorter than the time required
to transfer the information to the operational user. Hence, an accurate sea ice edge prediction as well as determination is
crucial for fine-scale geophysical modeling and for near-real-time operations. In this study, active contour modelling (known
as Snake model) and non-rigid motion estimation techniques have been used for predicting the sea ice edge (SIE) in the Antarctic.
For this purpose the SIE has been detected from sea ice concentration derived using special sensor microwave imager (SSM/I)
observations. The 15% sea ice concentration pixels are being taken as the edge pixel between ice and water. The external force,
gradient vector flow (GVF), of SIE for total the Antarctic region is parameterised for daily as well as weekly data set. The
SIE is predicted at certain points using a statistical technique. These predicted points have been used to constitute a SIE
using artificial intelligence technique, the gradient vector flow (GVF). The predicted edge has been validated with that of
SSM/I. It is found that all the major curvatures have been captured by the predicated edge and it is in good agreement with
that of the SSM/I observation. 相似文献
7.
Human activities in the karst Ozark Plateaus can impact water quality of springs where surface water is rapidly transferred
to subsurface conduits. Bennett Spring, in southern Missouri, is the fourth largest spring in the state and supports local
tourism activities. Questions regarding poorly functioning on-site wastewater systems (OWS) have raised concerns over the
long-term water quality of the spring. This study reports the results of a surface water quality monitoring program in the
recharge area where monthly samples were collected at base flow to identify potential pollution sources to the spring. Base
flow hydrology of the recharge area was highly variable over the study period, which was drier than normal, causing an incomplete
sampling record due to no flow conditions at some sites. For most of the year, nutrient levels were less than the eutrophic
threshold (ET) of 0.075 mg/l total phosphorus (TP) and 1.5 mg/l total nitrogen (TN). Sites that consistently displayed concentrations
of TP and TN higher than the ET were influenced by wastewater treatment plants (WTP) or OWS. Sites with nutrient concentrations
above the ET were likely influenced by the re-release of nonpoint source related TP and TN delivered to streams during storm
events. Water quality and discharge at the spring outlet remained consistent over the sampling period suggesting diffuse recharge
from a deep aquifer source is able to dilute shallow ground water sources carrying nonpoint pollutants at base flow. Historical
and regional data comparisons show these trends have been consistent over at least the last two decades. 相似文献
8.
Randhir Singh B. G. Vasudevan P. K. Pal P. C. Joshi 《Journal of Earth System Science》2004,113(1):89-101
Microwave sensor MSMR (Multifrequency Scanning Microwave Radiometer) data onboard Oceansat-1 was used for retrieval of monthly
averages of near surface specific humidity (Q
a) and air temperature (T
a) by means of Artificial Neural Network (ANN). The MSMR measures the microwave radiances in 8 channels at frequencies of 6.6,
10.7, 18 and 21 GHz for both vertical and horizontal polarizations.
The artificial neural networks (ANN) technique is employed to find the transfer function relating the input MSMR observed
brightness temperatures and output (Q
a andT
a) parameters. Input data consist of nearly 28 months (June 1999 – September 2001) of monthly averages of MSMR observed brightness
temperature and surface marine observations ofQ
a
andT
a
from Comprehensive Ocean-Atmosphere Data Set (COADS).
The performance of the algorithm is assessed with independent surface marine observations. The results indicate that the combination
of MSMR observed brightness temperatures as input parameters provides reasonable estimates of monthly averaged surface parameters.
The global root mean square (rms) differences are 1.0‡C and 1.1 g kg−1 for air temperature and surface specific humidity respectively. 相似文献
9.
Gandikota V. Rao 《Natural Hazards》1994,9(1-2):17-35
Tropical cyclones are notorious for their destruction. Because they occur mostly over oceans their structures are revealed only through aerial reconnaissance, radar or through satellites. The recently launched DMSP satellite (F8) has provided polarized microwave Brightness Temperatures, TB's. Using certain algorithms, rainrates and wind speeds were derived for a few typhoons.The 85 GHz TB's available at nearly 15 km intervals, disclosed that low values such as 230 K are registered within 2° of the advancing side of the center. These low TB's moved centerward as the typhoon developed further. They propagated rearwards as the storm weakened.Convective rainrates, defined as those equalling or exceeding 3 mm h–1, within the core, seem to set trends for the intensification. On the other hand convective rain outside the core had a negative effect on the storm. Similarly convective rainrates within the core of developing storms were significantly different from those of the weakening typhoons while the corresponding stratiform rainrates were not markedly different between intensifying and deintensifying ones. Some typhoons developed strong winds exceeding 30 m s–1 even as far from the center as 440 km. The derived speeds decreased in accuracy in rain situations.These preliminary results are to be interpreted with caution in view of the recency of the algorithms and the smallness of the sample. However, the hazards scientist would find the SSM/I data to be valuable in forewarning the public and in using these data for purposes such as surge forecasting. 相似文献
10.
Rupa Kamineni S. R. H. Rizvi S. C. Kar U. C. Mohanty R. K. Paliwal 《Journal of Earth System Science》2002,111(3):351-364
Oceansat-1 was successfully launched by India in 1999, with two payloads, namely Multi-frequency Scanning Microwave Radiometer
(MSMR) and Ocean Color Monitor (OCM) to study the biological and physical parameters of the ocean. The MSMR sensor is configured
as an eight-channel radiometer using four frequencies with dual polarization. The MSMR data at 75 km resolution from the Oceansat-I
have been assimilated in the National Centre for Medium Range Weather Forecasting (NCMRWF) data assimilation forecast system.
The operational analysis and forecast system at NCMRWF is based on a T80L18 global spectral model and Spectral Statistical
Interpolation (SSI) scheme for data analysis. The impact of the MSMR data is seen globally, however it is significant over
the oceanic region where conventional data are rare. The dry-nature of the control analyses have been removed by utilizing
the MSMR data. Therefore, the total precipitable water data from MSMR has been identified as a very crucial parameter in this
study. The impact of surface wind speed from MSMR is to increase easterlies over the tropical Indian Ocean. Shifting of the
positions of westerly troughs and ridges in the south Indian Ocean has contributed to reduction of temperature to around 30‡S. 相似文献
11.
Microalgal culture experiments to track chlorophyll-a (chl-a) transformation during senescence were characterised by the production of demetallated Type I chl-a transformation products in Pavlova gyrans and by the production of oxidative Type I transformation products in Isochrysis galbana. Dark-induced senescence in I. galbana produced a different distribution of Type I products from nutrient depletion induced senescence. Several novel Type I compounds were detected, including a chl-d like compound in I. galbana and a chl-a precursor like compound in P. gyrans. Type II chl-a transformation products were detected in the dissolved phase of I. galbana cultures; this is the first report of such compounds associated with marine algae. 相似文献
12.
Snow Water Equivalent (SWE) is an important parameter in hydrologic engineering involving the streamflow forecasting of high-elevation watersheds. In this paper, the application of classic Artificial Neural Network model (ANN) and a hybrid model combining the wavelet and ANN (WANN) is investigated in estimating the value of SWE in a mountainous basin. In addition, k-fold cross validation method is used in order to achieve a more reliable and robust model. In this regard, microwave images acquired from Spectral Sensor Microwave Imager (SSM/I) are used to estimate the SWE of Tehran sub-basins during 1992–2008 period. Also for obtaining measured SWE within the corresponding Equal-Area Scalable Earth-Grid (EASE-Grid) cell of SSM/I image, approach of Cell-SWE extraction using height–SWE relations is applied in order to reach more precise estimations. The obtained results reveal that the wavelet-ANN model significantly increases the accuracy of estimations, mainly because of using multi-scale time series as the ANN inputs. The Nash–Sutcliffe Index (NSE) for ANN and WANN models are respectively 0.09 and 0.44 which shows a firm improvement of 0.35 in NSE parameter when WANN is applied. Similar trend is observed in other parameters including RMSE where the value is 0.3 for ANN and 0.07 for WANN. 相似文献
13.
Auto-correlation analysis of ocean surface wind vectors 总被引：1，自引：0，他引：1
Abhijit Sarkar Sujit Basu A. K. Varma Jignesh Kshatriya 《Journal of Earth System Science》2002,111(3):297-303
The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different
measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measuredin situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month
of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall of the autocorrelation
in the first few hours with a decorrelation time scale of about 6 hours. For a meaningful comparison between satellite derived
products andin situ data, satellite data acquired at different time intervals should be used with appropriate ‘weights’, rather than treating
the data as concurrent in time. This paper presents a scheme for temporal weighting using the auto-correlation analysis. These
temporal ‘weights’ can potentially improve the root mean square (rms) deviation between satellite andin situ measurements. A case study using the TRMM Microwave Imager (TMI) and Indian Ocean buoy wind speed data resulted in an improvement
of about 10%. 相似文献
14.
This paper compares features of unambiguous tectonic serpentinite mélanges (TSM) or serpentinite shear zones in the Coast Range ophiolite, Franciscan subduction complex, of coastal California and Sierra City Mélange of the northern Sierra Nevada of northeastern California with undisputed sedimentary serpentinite mélange (SSM) of the Great Valley Group (GVG) forearc basin deposits of coastal California, and with Franciscan serpentinite mélanges of disputed (sedimentary versus tectonic) origin. The GVG sedimentary serpentinite mélanges and disputed Franciscan serpentinite mélanges share strongly similar matrix textures and block-matrix relationships at scales from tens of meters or more to petrographic scale but differ significantly from serpentinite shear zones and TSM. This comparison suggests shared (non-diagnostic) and distinguishing features of TSM versus SSM. Internal bedding or foliation in blocks is oriented subparallel to mélange boundaries and matrix foliation for both TSM and SSM both may have strongly foliated matrix and both may feature localized shearing in matrix around block borders, especially if an SSM underwent significant post-depositional deformation. The same holds true for deformation and dismemberment of blocks, which is the block-forming and mixing mechanism in TSM but variably exhibited in SSM. In contrast only SSM have blocks or clasts whose internal foliation or bedding terminates abruptly along clast/block boundaries with a mismatch in mineralogy and/or lithology across such boundaries. Matrix foliation cuts blocks/clasts in TSM but not in SSM. SSM may show block/grain size grading but not TSM. SSM have exotic blocks and blocks may span a range of metamorphic grade, whereas TSM lack exotic blocks and blocks are isofacial. 相似文献
15.
NAVEEN R SHAHI NEERAJ AGARWAL ALOKE K MATHUR ABHIJIT SARKAR 《Journal of Earth System Science》2011,120(3):337-345
An atmospheric correction method has been applied on sea surface temperature (SST) retrieval algorithm using Very High Resolution
Radiometer (VHRR) single window channel radiance data onboard Kalpana satellite (K-SAT). The technique makes use of concurrent
water vapour fields available from Microwave Imager onboard Tropical Rainfall Measuring Mission (TRMM/TMI) satellite. Total
water vapour content and satellite zenith angle dependent SST retrieval algorithm has been developed using Radiative Transfer
Model [MODTRAN ver3.0] simulations for Kalpana 10.5–12.5 μm thermal window channel. Retrieval of Kalpana SST (K-SST) has been
carried out for every half-hourly acquisition of Kalpana data for the year 2008 to cover whole annual cycle of SST over Indian
Ocean (IO). Validation of the retrieved corrected SST has been carried out using near-simultaneous observations of ship and
buoys datasets covering Arabian Sea, Bay of Bengal and IO regions. A significant improvement in Root Mean Square Deviation
(RMSD) of K-SST with respect to buoy (1.50–1.02 K) and to ship datasets (1.41–1.19 K) is seen with the use of near real-time
water vapour fields of TMI. Furthermore, comparison of the retrieved SST has also been carried out using near simultaneous
observations of TRMM/TMI SST over IO regions. The analysis shows that K-SST has overall cold bias of 1.17 K and an RMSD of
1.09 K after bias correction. 相似文献
16.
以1996年7月我国南方暴雨水灾为例,研究了暴雨水灾时星载微波SSM/I的遥感数据,分析了SSM/I7个通道辐射亮度温度的极化散射和辐射特征,定义了识别降雨的散射指数SI,水灾警戒指数FI,和辐射极化指数PI.用SSM/I的观察数据,讨论了暴雨水灾时这些指数的时间和空间的特征性变化,给出了SSM/I数据对于1996年7月暴雨和水灾的识别,以及全月降雨异常值的空间分布。 相似文献
17.
Ananda K. Das U. C. Mohanty Someshwar Das M. Manual S. R. Kalsi 《Journal of Earth System Science》2003,112(2):165-184
The skill and efficiency of a numerical model mostly varies with the quality of initial values, accuracy on parameterization
of physical processes and horizontal and vertical resolution of the model. Commonly used low-resolution reanalyses are hardly
able to capture the prominent features associated with organized convective processes in a monsoon depression. The objective
is to prepare improved high-resolution analysis by the use of MM5 modelling system developed by the Pennsylvania State University/National
Center for Atmospheric Research (PSU/NCAR). It requires the objective comparison of high and low-resolution analysis datasets
in assessing the specific convective features of a monsoon depression. For this purpose, reanalysis datasets of NCAR/NCEP
(National Center for Atmospheric Research/National Centers for Environmental Prediction) at a horizontal resolution of 2.5‡
(latitude/longitude) have been used as first guess in the objective analysis scheme. The additional asynoptic datasets obtained
during BOBMEX-99 are utilized within the assimilation process. Cloud Motion Wind (CMW) data of METEOSAT satellite and SSM/I
surface wind data are included for the improvement of derived analysis. The multiquadric (MQD) interpolation technique is
selected and applied for meteorological objective analysis at a horizontal resolution of 30 km. After a successful inclusion
of additional data, the resulting reanalysis is able to produce the structure of convective organization as well as prominent
synoptic features associated with monsoon depression. Comparison and error verifications have been done with the help of available
upper-air station data. The objective verification reveals the efficiency of the analysis scheme. 相似文献
18.
简单介绍了微波辐射的原理与应用现状,利用美国国防气象卫星计划DMSP F系列卫星携带的SSM/I辐射计南极地区极投影网格亮温数据进行了分析与处理。结合微波亮温等温线图和南极等高线图分析了南极地区亮温分布的特点。选取8个特征区域,对1992-2000年的日亮温数据进行了时间序列分析,分析了冰盖和冰架的亮温特性、季节和年度变化、短期波动等特征。研究表明南极大陆外围冰架和南极半岛地区的亮温呈增高趋势,而内陆冰盖地区则保持相对稳定;揭示了近年来随全球气候的变暖,南极冰架和南极半岛的融化正在加剧的趋势。 相似文献
19.
2000-2014年西藏雅鲁藏布江流域积雪时空变化分析及对气候的响应研究 总被引：7，自引：6，他引：1
利用2000-2014年MODIS逐日无云积雪产品对雅鲁藏布江流域积雪特征的空间分布及变化、积雪随高程变化的规律进行了分析,并采用被动微波数据SMMR （1979-1987年）和SSM/I （1988-2008年）以及中国地面降水和气温0.5°×0.5°日值格点数据集,研究了雅鲁藏布江流域关键积雪参数对气候要素的响应等。结果表明：流域下游积雪日较大且变化剧烈;流域整体上呈显著减少的趋势;积雪日随高程的上升而增加;流域内降水呈不显著的增加趋势,而气温呈显著的增加趋势,最高气温对积雪变化影响最大;气温对积雪终日的影响明显高于积雪初日;在积雪消融期降水的增多促进了积雪的消融。 相似文献
20.
Variations in Alpine white mica 40Ar/39Ar dates from the cover units of the Siviez-Mischabel Nappe relate to regional variations in the thermal history of the nappe. We focus on three regions within the nappe: the central Siviez-Mischabel (CSM), the southern Siviez-Mischabel (SSM), and the eastern Siviez-Mischabel (ESM). Our approach weaves together observations of quartz and mica textures in thin section, the variation of 40Ar/39Ar date with grain size, considerations of the effective diffusion dimension (EDD) of argon in white mica, and a comparison of dates with diffusion model results. In the CSM, pressure solution of quartz and dislocation glide in mica accommodated Alpine deformation. Dates record mica growth during nappe emplacement from 40 to 36 Ma and do not vary with grain size. In the SSM and ESM, both mica and quartz show textures associated with dynamic recrystallization, and dates decrease with grain size. In the SSM, dates also agree with the timing of nappe emplacement, but in the ESM, dates significantly post-date the timing of nappe emplacement. A comparison of dates with diffusion model results supports inferences from rock fabrics that the SSM experienced higher peak temperatures than the CSM, even though dates from both units approximate the timing of mica growth. Dates obtained from the ESM, however, do not compare well with simple models, and the thermal evolution of this region of the nappe, in the neighborhood of the Simplon Fault Zone, is not well understood. 相似文献