NISCAIR Online Periodicals Repository Collection: IJRSP Vol.36(2) [April 2007]

Rainfall retrieval from TRMM radiometric channels using artificial neural networks

Thu, 29 Mar 2007 22:58:59 GMT

Title: Rainfall retrieval from TRMM radiometric channels using artificial neural networks

Authors: Kumar, Rajesh; Das, I M L; Gairola, R M; Sarkar, A; Agarwal, Vijay K

Abstract: An algorithm for the retrieval of rainfall has been developed from the radiometric measurements of TRMM microwave Imager (TMI) of Tropical Rainfall Measuring Mission (TRMM) satellite using multilayer feed forward Artificial Neural Network (ANN) over different oceanic and land regions of India and its neighborhoods. The “back propagation with momentum” has been used as a learning algorithm for the ANN architecture. The inputs to the ANN are TMI-brightness temperatures (T_B) and the output TMI-rain rates, to demonstrate its capability to retrieve rain rates within limited computer time and with reasonable accuracy. The training data has been split up randomly in three parts, viz. training, validation and test data sets. The performance of the network is evaluated for independent data sets (which were not included in the training) after training and cross validation. Instantaneous precipitation estimates demonstrate very high correlation coefficients with the observed rainfall. Although the rainfall estimation using ANN are influenced by many factors such as the representativeness and sufficiency of the training dataset, the generalization capability of the network to new data sets, seasonal and location changes, it is found that the model can still be used for the retrieval of precipitation at high spatial and temporal resolutions. The ANN is shown to quickly reproduce the results of a long time series of data. The ANN derived rain rates have been compared with the estimates obtained from non-linear multivariate regression (MR) techniques using the identical set of data. It has been found that the ANN method, in general, is far superior to the MR technique in its ability to reproduce rainfall intensity in very short time.

Page(s): 114-127

Observations of ULF/ELF anomalies detected by DEMETER satellite prior to earthquakes

Thu, 29 Mar 2007 22:58:59 GMT

Title: Observations of ULF/ELF anomalies detected by DEMETER satellite prior to earthquakes

Authors: Bhattacharya, S; Sarkar, S; Gwal, A K; Parrot, M

Abstract: Seismo-electromagnetic effects refer to the electric and magnetic field perturbations found during the course of earthquakes. Furthermore, in the range of electromagnetic emissions, stress is laid on the ultra low frequency (ULF) and extremely low frequency (ELF), due to their reasonably higher penetration depth as compared to the other higher frequencies. The emissions are observed prior to moderate and strong earthquakes. One of the most promising diagnostic tools for studying the electromagnetic anomalies is using satellite based technique. Some important electric field variations observed prior to two individual earthquakes are discussed in this paper, one in Arunachal Pradesh, India (28.87°N, 94.60°E, 20:06:42 hrs UTC) measuring 5.9 and the other in the west coast of Columbia (6.86°N, 77.8°W, 20:50:46 hrs UTC) measuring a stronger 6.2 on the Richter scale. The anomalies are reported to occur in the ULF/ELF range. The observations have been detected prior to both the events using the low altitude satellite DEMETER (height ≈710 km), which is aimed at studying the ionospheric perturbations related to earthquakes and volcanic eruptions.

Page(s): 103-113

Implementation of multilayer ferrite radar absorbing coating with genetic algorithm for radar cross-section reduction at X-band

Thu, 29 Mar 2007 22:58:59 GMT

Title: Implementation of multilayer ferrite radar absorbing coating with genetic algorithm for radar cross-section reduction at X-band

Authors: Parida, Ramesh C; Singh, D; Agarwal, N K

Abstract: Genetic algorithm (GA) approach has been analyzed to optimize the thickness of various layers as well as selection of suitable ferrite material for better absorption and reduction of radar cross-section (RCS) at X-band frequency. For this purpose, the available ferrite materials with frequency-dependent permittivities ε(ƒ) and permeabilities μ(ƒ) have been used as data base. An empirical relationship has been developed between µ and ƒ as well as ε and ƒ for application of GA to select the proper ferrite material at particular frequency range for minimum reflection or maximum absorption and reduction of RCS. The GA has advantage that, with fitness function, it places an upper bound on the total thickness of the coating as well as on the number of layers contained in the coating. This greatly simplifies manufacturing of absorber in the form of sheet by coating ferrite material. Four-layer coating with different thickness and different ferrite materials has been simulated by GA and the results obtained with GA have been synthesized on aluminum plate. The paint for coating over aluminum sheet has been prepared by mixing the known ferrite powders (used in data base) with glass epoxy resin with suitable amount of hardener. The absorption has been measured by absorber testing device (ATD) method and RCS has been measured by monostatic radar measurements at X-band (8-12 GHz) in anechoic chamber. The absorption and RCS were measured after each layer of coating. A considerable amount of reduction of RCS and absorption is observed as compared to the plain aluminum sheet at X-band.

Page(s): 145-152

Annual cycle of surface meteorological and solar energy parameters over Orissa

Thu, 29 Mar 2007 22:58:59 GMT

Title: Annual cycle of surface meteorological and solar energy parameters over Orissa

Authors: Mohapatra, G N; Panda, U S; Mohanty, P K

Abstract: Surface meteorological and solar energy parameters over Orissa are studied using observed data from India Meteorological Department (IMD) and National Aeronautics and Space Administration Surface meteorology and Solar Energy (NASA SSE) data set. The observed data are mostly on surface meteorological parameters over 17 meteorological stations over Orissa. SSE data set, Release 3, is a satellite and reanalysis derived 10 year climatology (July 1983-June 1993) available on global grid mesh of 1° and consisting of both surface meteorological and solar energy parameters. The usefulness of NASA data set for the Orissa regions are examined by comparing it with IMD data. Comparative views of the annual cycle of both the data sets reveal the intensities and periods of extremes and their relative agreements /disagreements in the course of the annual cycle. Closeness of fit and coherence between the two data sets are examined through scatter plots and cross-spectral analysis, respectively. The results show a better goodness of fit between IMD and NASA data set in air temperature and lowest standard error of estimate in wind speed. Cross-spectrum analysis shows very good coherence between IMD and NASA data in the annual and semi-annual bands but lesser coherence in the intra-seasonal band. The results suggest that NASA data, when used in conjunction with good quality observed data, can make it possible to assess the renewable energy potential of different districts in Orissa, besides its use for weather and climate study.

Page(s): 128-144