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The stability of a viscoelastic fluid in a densely packed horizontal porous layer heated from below is considered using an Oldroyd model. Critical Rayleigh number, wave number, and frequency for overstability are determined by applying the linear stability theory. It is shown that the critical Rayleigh number is invariant under all relevant boundary combinations. Also, it is found that the effect of elasticity of the fluid is to destabilize the system and that of porosity is to stabilize the same. The limiting case of very high Prandtl number and the degenerate case corresponding to the Maxwell model are analyzed in some detail.

The IRS-P6 satellite has multi-resolution and multispectral capabilities on a single platform. A continuous and autonomous co-registration and geolocation of image data from different sensors with widely varying view angles and resolution is one of the unique challenges of IRS-P6 data processing. This requires in-flight geometric calibration of the cameras. In-flight calibration includes alignment calibration of individual sensors and calibration between the sensors. A method for in-flight geometric calibration and quality assessment of IRS-P6 images is presented in this paper. The objectives of this study are to ensure the best absolute and relative location accuracy of different cameras, and the same location performance with payload steering and co-registration of multiple bands. This is done using a viewing geometry model, given ephemeris and attitude data, precise camera geometry and datum transformation. In the model, the forward and reverse transformations between the coordinate systems associated with the focal plane, payload, body, orbit and ground are rigorously and explicitly defined. System-level tests using comparisons to ground check points have validated the operational geolocation accuracy performance and the stability of the calibration parameters.

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The linear stability of a viscoelastic fluid-saturated sparsely packed porous layer heated from below is studied analytically using the Darcy–Brinkman–Jeffreys model with different boundary combinations. The Galerkin technique is employed to determine the criterion for the onset of oscillatory convection. The effects of the viscoelastic parameters, the Prandtl number, and the porous parameter on the critical Rayleigh number, the wave number, and the frequency are analyzed. The results are compared with those obtained for both a Darcy–Jeffrey fluid and a Maxwell fluid. It is shown that under certain conditions for the viscoelastic parameters, the flow is overstable. The possibility of the occurrence of bifurcation is also discussed.