In this work, we introduce an image enhancement method ideally suited for the visualization of coronal intensity images. The steep radial gradient of the coronal brightness is adjusted by normalising the coronal image with the Fourier approximation of its local average. A method based on deconvolution and localised normalising of the data at many different spatial scales is used to further enhance the fine structures, and a wavelet shrinkage denoising method is used for noise suppression. The effectiveness of this method is demonstrated on a series of images observed by various instruments including spacial and earth-based coronagraphs as well as photos during total solar eclipse. This method is very helpful for qualitative analysis of solar coronal structures that are mostly invisible on original images.
We have developed a new narrowband tunable filter to perform imaging spectroscopy of the solar chromosphere.
Using Liquid Crystal Variable Retarders (LCVRs) as the tuning elements for wavelength, wide-band polarizers
and super achromatic half-wave plates, it is possible to make high speed tuning (about 0.1Sec), to exclude
mechanical drives (and oil tank), and to cover a wide wavelength range (510-100nm). This filter builds up
with seven stages each consisting of a pair of calcites, LCVR, half-wave plates and linear polarizer. The full
width at half maximum (FWHM) of the filter transmission is about 0.025nm at 656.3nm.We demonstrate that
the concept of the universal tunable filter using the LCVR's as tuning elements is highly promising for future
application to space mission and ground based observations.