Imaging spectroscopy of Mars during 1990

We conducted an extensive program of Mars observations during the recent 1990 opposition utilizing three telescopes at the Mauna Kea Observatory, Hawaii. Images and spectra were obtained between 0.4 and 4.0 μm using a CCD camera (0.4–1.0 μm, two grating array spectrometers (0.5–0.95 μm and 2.1–2.5 μm), and a near‐infrared array camera (1.3–4.05 μm). Our goals were to take advantage of the good ground‐based spatial resolution possible from this opposition, the best until 2001, and to try to map spatial variations in subtle spectral absorption features caused by martian atmospheric volatiles and trace gases and by surface minerals such as ferric oxides, clays, and pyroxenes. Some preliminary results of our imaging observations are presented in Figure 1. These images were obtained in November 1990 using the University of Hawaii 61‐cm telescope and an uncooled CCD camera/narrowband filter wheel combination (0.40‐μm image), and the NASA 3.0‐m Infrared Telescope Facility's ProtoCAM array camera (2.00‐μm and 3.02‐μm images). ProtoCAM uses a 58×62 element Indium‐Antimonide (InSb) array and three cooled circular variable filters sensitive from 1.3–5.8 μm. We obtained images of the entire martian disk in 58 colors from 1.3–2.5 μm (0.9% spectral resolution) and in 25 colors from 2.9–4.05 μm (1.4% spectral resolution). These observations were made 2 weeks before opposition (phase angle 12°) when Mars was in late northern winter (L_s = 333°) and had an angular size of 18 arc sec. The 0.4 μm image was obtained 2 weeks later, closer to opposition (phase angle 2°, L_s = 341°).