We present first results from the newly developed remote sensing instrument CLEO (CLear Sky Observatory). CLEO
consists of a commercially available CCD miniature spectrometer (Hamamatsu C10082CAH) and foreoptics to measure
the global and diffuse solar irradiance. The irradiance is measured through a teflon diffuser. The diffuse irradiance is
obtained moving a 180° metal band in the optical path to block the solar direct beam. CLEO measures simultaneously
UV and Visible radiation from 163nm to 845nm, in steps of 0.3nm with a resolution of 1nm. The spectrometer is
temperature controlled to 10°C to stabilize its optical properties. The dark count is frequently measured using a
motorized four positions filterwheel with an opaque disc at one position that acts as a shutter used to block the light
input. The system automatically adjusts the integration time to optimize the signal-to-noise. Another difference to
previous shadowband instruments is that CLEO moves the shadowband over the whole hemisphere instead of just a few
positions in and around the sun's direction. This has the advantage of simplifying the installation procedure and solves
the problem with the shadow only partially covering the diffuser due to instrument misalignment.
The Earth Atmospheric Solar-Occultation Imager (EASI) is a proposed interferometer with 5 telescopes on an 8-meter boom in a 1D Fizeau configuration. Placed at the Earth-Sun L2 Lagrange point, EASI would perform absorption spectroscopy of the Earth’s atmosphere occulting the Sun. Fizeau interferometers give spatial resolution comparable to a filled aperture but lower collecting area. Even with the small collecting area the high solar flux requires most of the energy to be reflected back to space. EASI will require closed loop control of the optics to compensate for spacecraft and instrument motions, thermal and structural transients and pointing jitter. The Solar Viewing Interferometry Prototype (SVIP) is a prototype ground instrument to study the needed wavefront control methods. SVIP consists of three 10 cm aperture telescopes, in a linear configuration, on a 1.2-meter boom that will estimate atmospheric abundances of O2, H2O, CO2, and CH4 versus altitude and azimuth in the 1.25 - 1.73 micron band. SVIP measures the Greenhouse Gas absorption while looking at the sun, and uses solar granulation to deduce piston, tip and tilt misalignments from atmospheric turbulence and the instrument structure. Tip/tilt sensors determine relative/absolute telescope pointing and operate from 0.43 - 0.48 microns to maximize contrast. Two piston sensors, using a robust variation of dispersed fringes, determine piston shifts between the baselines and operate from 0.5 - 0.73 microns. All sensors are sampled at 800 Hz and processed with a DSP computer and fed back at 200 Hz (3 dB) to the active optics. A 4 Hz error signal is also fed back to the tracking platform. Optical performance will be maintained to better than λ/8 rms in closed-loop.
The radiometer CLIMAT is a highly sensitive field instrument designed for multispectral thermal infrared measurements.
Ground-based measurements can be performed. but the instrument has capabilities for operating from aircraft or balloon.
The optics consist of an objective lens and a condenser mounted according to the Koehler principle to provide uniform irradiation
over the detector surface. The radiometric signal is treated by a fast thermopile detector characterized by a low noise and a very
weak temperature dependence of its responsivity. The managing system allows either manual or automated measurements. The
energy consumption of the instrument is optimized for a maximum autonomy.
The optical and electrical units of the instrument are described. Different experimental studies for measuring the sensitivity
accuracy, spectral characteristics, thermal behavior and, field of view of the instrument are described.
The instrument is dedicated to ground and vegetation on the one hand. and on the other hand, clouds and atmospheric soundings.
The radiometer is also designed for calibrations or analyses of satellite radiometry data.
Some atmospheric measurements obtained with a prototype are presented.
Prospects are the development and the qualification of a narrow field-of-view instrument adapted to inhomogeneous targets
such as cirrus clouds. A 3.7-tim channel and an internal blackbody are under study.