Hala K. Al Jassar

The spatial density gradient of galactic cosmic rays and its solar cycle variation observed with the Global Muon Detector Network

We derive the long-term variation of the three-dimensional (3D) anisotropy of approximately 60 GV galactic cosmic rays (GCRs) from the data observed with the Global Muon Detector Network (GMDN) on an hourly basis and compare it with the variation deduced from a conventional analysis of the data recorded by a single muon detector at Nagoya in Japan. The conventional analysis uses a north-south (NS) component responsive to slightly higher rigidity (approximately 80 GV) GCRs and an ecliptic component responsive to the same rigidity as the GMDN. In contrast, the GMDN provides all components at the same rigidity simultaneously. It is confirmed that the temporal variations of the 3D anisotropy vectors including the NS component derived from two analyses are fairly consistent with each other as far as the yearly mean value is concerned. We particularly compare the NS anisotropies deduced from two analyses statistically by analyzing the distributions of the NS anisotropy on hourly and daily bases. It is found that the hourly mean NS anisotropy observed by Nagoya shows a larger spread than the daily mean due to the local time-dependent contribution from the ecliptic anisotropy. The NS anisotropy derived from the GMDN, on the other hand, shows similar distribution on both the daily and hourly bases, indicating that the NS anisotropy is successfully observed by the GMDN, free from the contribution of the ecliptic anisotropy. By analyzing the NS anisotropy deduced from neutron monitor (NM) data responding to lower rigidity (approximately 17 GV) GCRs, we qualitatively confirm the rigidity dependence of the NS anisotropy in which the GMDN has an intermediate rigidity response between NMs and Nagoya. From the 3D anisotropy vector (corrected for the solar wind convection and the Compton-Getting effect arising from the Earth’s orbital motion around the Sun), we deduce the variation of each modulation parameter, i.e., the radial and latitudinal density gradients and the parallel mean free path for the pitch angle scattering of GCRs in the turbulent interplanetary magnetic field. We show the derived density gradient and mean free path varying with the solar activity and magnetic cycles.

Assessment of shuttle radar topographic mission performance over the Kuwait desert terrain

Forty-three digital elevation models (DEMs) of the Managesh oil field, Kuwait desert study area, are derived from 28 advanced synthetic aperture radar (ASAR) images using radar interferometry (InSAR) technique. Weighted-average technique is used to reduce the noise in the integrated DEM. The final DEM is compared with DEM of Shuttle Radar Topography Mission (SRTM) and found to have a general agreement. The standard deviation (STD) of individual DEMs with reference to DEM of SRTM is in the range 10 to 40 m. The results indicate that the 90 m spatial resolution DEM of SRTM is noisier over the Managesh oil field as it shows drastic changes in elevations of neighboring pixels which is not expected for a plain desert like the Managesh oil field. Using mean filter, the noise level is estimated as one meter. The reasons for high noise in the DEM of SRTM may be due to uneven distribution of soil moisture leading to uneven penetration of microwaves. The results are in confirmation with the earlier investigators as explained in the text.

Observation of atmospheric effects on repeat-pass interferometric synthetic aperture radar over the Kuwait desert

Twenty-eight advanced synthetic aperture radar (ASAR) scenes from the Environmental Satellite (ENVISAT) are analysed to select suitable pairs for generating a digital elevation model (DEM) and displacement maps. For this purpose, the repeat-pass interferometric synthetic aperture radar (InSAR) technique is implemented using GAMMA interferometric modules. The perpendicular component of baseline (B┴) is taken as the criteria for selecting the pairs: 0 < B┴ <100 m for displacement maps and 200 < B┴ < 400 m for the DEM. Though there are many pairs satisfying the above criteria, only four case studies are presented here to illustrate the effects of atmosphere on the DEM and displacement maps over the Kuwait desert climate. In each case study, two examples are selected: one where the atmosphere is a serious problem and another example the atmosphere has no significant problem. The DEM of the Shuttle Radar Topographic Mission (SRTM) is taken as a reference for root mean square (RMS) error estimation in the DEM. The RMS error varies from as low as 2 m to as high as 40 m. Some DEMs showed fringe-like structures resembling precipitable water vapour (PWV) fields. Similarly, the measured displacement values were found to vary randomly from place to place and time to time. The displacement maps showed vertical structures similar to PWV. The DEM was corrected for PWV. The results are encouraging. From this study, it is clear that, even for desert areas, there is a need to look into the effects of PWV on the DEM and displacement maps before the results are used.

Study on spatial variation of land subsidence over Minagish–Umm Gudair oil fields of Kuwait using synthetic aperture radar interferometry technique

Abstract. Land subsidence can be a major problem where there are large-scale underground activities such as oil extraction. This paper addresses the spatial variability of land subsidence over Minagish and Umm Gudair oil fields of Kuwait. Synthetic aperture radar interferometry (InSAR) with multiple reference scenes using a persistent scatterer InSAR toolchain was employed in this study. Twenty-nine scenes of advanced synthetic aperture radar data (for the period January 2005 to August 2009) were used to make 20 pairs of interferograms (with high coherence and low noise) of stable point-like reflectors. The output of this study is the land subsidence maps of Minagish and Umm Gudair oil fields with a spatial resolution of 40 m. The results indicate that there is land subsidence of 29.9  mm/year in the southern part of the oil field (Umm Gudair). This is the first detailed assessment of land subsidence in the Minagish–Umm Gudair oil fields; therefore, no ground-truth data are available to compare the subsidence results. The results were consistent, indicating their validity.

Analysis of advanced synthetic aperture radar data for geometric accuracy and backscattering signatures over the Kuwait desert

Seven scenes of ASAR images acquired by ENVISAT satellite during the time period April 2004 - June 2005 have been analyzed to assess the geo-coding accuracy of the data. Eighty ground control points (GCPs) spread all over Kuwait were measured using Trimble 5700 GPS which are mainly the road intersections. The same road intersections were identified in the ASAR image and its geo-locations were measured using BEST software package provided by the European Space Agency. The GPS and BEST results were compared to estimate the geo-location accuracy of ASAR data. The average accuracy in geo-coding is estimated to be 54 m in both azimuth and range directions. These results are in agreement with the results reported in the literature. Twenty well-defined targets (built-up areas, grass lands, airports, agricultural plots, desert soils, etc.) were considered for the backscattering signature study. The size of each target varies from 50,000 to 100,000 Single Look Complex (SLC) pixels for good statistical accuracy. It has been estimated that the Standard Deviation (Std) of backscatter signature is 1.3% (after speckle filtering) of the mean value. The temporal / spatial variability of the signatures are within the Std. During the study period, the soil moisture varied from 6% to 10% as estimated from AMSR-E on board Acqua satellite.

Analysis of ASAR data for geo-location accuracy and desert signatures

The utility of ASAR data will be greately enhanced if the Radiometric and Geometric quality of the data satisfies the requirements of applications. 7 secenes of ASAR data acquired during April 2004 - June 2005 have been processed to assess the Geo-location accuracy and also temporal / spatial variability of backscattered signatures. Ground Crontrol Points (GPS) approach was used for Geometric accuracy assessment. 80 GCPs spread all through the image were measured using Trimble 5700. It is estimated that the geometric accuracy of the data is within 55 m. This is in agreement with the reported accuracies in the literature. About 20 well defined targets were considered for the backscattering signature study. The size of each target varies from 1000 to 5000 SLC pixels for good statistical stability of the signature. It has been estimated that the Standard Deviation (STD) of the sitgnature is 1.3% and the temporal / spatial variability of the signatures ( considering all varieties of targets such as built-up area, grass lands, airports, agricultureal plots, desert soils, etc) are within its STD. During this study period the soil moisture varied from 10% to 6% as recorded from AMSR-E on board Acqua satellite.The ASAR data has been filtered for speckle noise.

High-energy cosmic ray modulation associated with interplanetary shocks observed by the GMDN

Interplanetary shocks are caused both by interplanetary counterparts of coronal mass ejections (ICMEs) and by co-rotating interaction regions (CIRs) propagating in the interplanetary medium. CIRs are formed by the interaction between high-speed and slow solar wind streams. When the interplanetary disturbance propagates faster than the magnetosonic wave speed, in the solar wind frame, a shock wave is formed. Shocks frequently produce decreases of cosmic rays observed both by neutron monitors and muon detectors located at the Earth’s surface. In this work, we analyze this kind of modulation of high-energy cosmic rays (> 50 GeV) observed by the Global Muon Detector Network (GMDN). After correcting both the atmospheric temperature and pressure effects, we calculated the isotropic intensity and the anisotropy vector. From a list of 38 interplanetary shocks identified in 2015 using interplanetary magnetic field and plasma parameters, we performed a superposed epoch analysis grouping the events by type and orientation of shocks. We found that the cosmic ray isotropic intensity is higher when it is associated to fast forward shocks when compared to fast reverse shocks. We also identified some differences in the anisotropy vector when comparing different types of shocks or shocks that are quasi-perpendicular with the remaining ones.

Average features of the interplanetary shock observed with the Global Muon Detector Network (GMDN)

From three-dimensional spatial density gradient of galactic cosmic rays (GCRs) observed with the Global Muon Detector Network (GMDN), we derive average features of the GCR depleted region behind the IP (interplanetary) shock. We identify 207 IP-shocks that passed the earth based on the geomagnetic storm sudden commencements (SSCs) and extract 50 events that are associated with solar coronal mass ejections (CMEs) in a period between 2006 and 2014. From the first order GCR anisotropy corrected for the solar wind convection and Compton-Getting effect arising from the earth’s orbital motion, we deduce the density gradient on an hourly basis for each event. We then derive the average temporal variation of the density gradient by superposing its variations at the SSC onset timing. We confirm that the density gradient components are clearly enhanced after the shock passage, indicating the existence of GCR depleted region behind the shock which causes the Forbush Decrease in the cosmic ray intensity. The enhancement of the radial gradient shows longer duration when the earth has encountered the western flank of the shock, implying an asymmetric shielding effect of the shock on the GCRs. The longitudinal gradient, on the other hand, shows that the GCR density minimum is located around the longitudinal center behind the shock, which can be ascribed to the centered ejecta driving IP-shock.

Time Series Analysis of the Digital Elevation Model of Kuwait Derived from Synthetic Aperture Radar Interferometry

The digital elevation model derived from SAR Interferometry is prone to atmospheric, penetration into soil medium, system noise and decorrelation errors. Eight ASAR images are selected for this study which have unique data set forming 7 InSAR pairs with single master image. It is expected that all the DEMs should have the same elevation values spatially with in the noise limits. However, they differ very much with one another beyond the noise levels indicating the effects of atmosphere and other disturbances. The 7 DEMs are compared with the DEM of SRTM for the estimation of errors. The spatial and temporal distribution of errors in DEM are analyzed by considering several case studies.