6. Conclusion and outlook
Two-dimensional imaging of the Sun with high spatial resolution was possible already for some time. High spectral resolution together with high spatial resolution is becoming feasible. Here we have analyzed narrow-band images in the wings of the Na D2 line with the aim at studying the variation of the granular temperature structure with atmospheric height. We have presented ways of image restoration which lead to a substantial increase of information on small-scale structures seen in narrow wavelength bands. Using linear combinations of high resolution images, to better discriminate between formation heights, we could visualize the disappearance of the granulation with increasing height. This confirms earlier results by Kneer et al. (1980, see also Nesis 1985 and references there) as well as Espagnet et al. (1995). We could not see any anti-correlation between intensity fluctuations formed in deep and higher layers.
We will continue analysing the time sequences from which the present data sets are taken. The method of two-dimensional spectroscopy with image restoration will then develop its full advantage over spectroscopy with conventional slit-spectrographs in studying small-scale processes in the solar atmosphere. While the intensity pattern formed in high layers (150 km) appears to have no ordered structure, this may be different when following their temporal evolution. Also, preliminary Dopplergrams with high spatial resolution, obtained from differences of images in the blue and red flank of Na D2, show interesting small-scale features.
Restoration of narrow-band images gives new insight into the dynamic processes of the solar atmosphere. Yet, the smaller the bandwidth the larger is the photon noise. Thus, for high spatial, spectral, and temporal resolution large telescopes are needed.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999