Estimation of water column optical properties and seafloor reflectance (532 nm) is demonstrated using recent SHOALS data collected at Fort Lauderdale, Florida (November, 2003). To facilitate this work, the first radiometric calibrations of SHOALS were performed. These calibrations permit a direct normalization of recorded data by converting digitized counts at the output of the SHOALS receivers to input optical power. For estimation of environmental parameters, this normalization is required to compensate for the logarithmic compression of the signals and the finite frequency of the bandpass of the detector/amplifier. After normalization, the SHOALS data are used to estimate the backscattering coefficient, the beam attenuation coefficient, the single-scattering albedo, the VSF asymmetry, and seafloor reflectance by fitting simulated waveforms to actual waveforms measured by the SHOALS APD and PMT receivers. The resulting estimates of these water column optical properties are compared to in-situ measurements acquired at the time of the airborne data collections. Images of green laser bottom reflectance are also presented and compared to reflectance estimated from simultaneously acquired passive spectral data.
The Stratospheric Wind Interferometer For Transport studies (SWIFT) is a passive sensor designed to measure winds in the stratosphere from a satellite. It is a field-widened Michelson interferometer very similar to the WINDII instrument on UARS but operates in the mid-IR, where it detects the Doppler shifts of atmospheric thermal emission lines of ozone. SWIFT uses a HgCdTe array detector to view the emission at the Earth's limb. Measurements are subsequently inverted by computer to obtain true vertical profiles of the stratospheric wind in the altitude range 20 to 40 km. Two orthogonal fields of view allow wind vectors to be obtained by combining the components observed from different directions a few minutes apart. Prototype Ge wafer etalon filters and a field-widened Michelson interferometer for the Mid-IR have been built and tested, with good results. Modeling studies indicate that a measurement precision of 5 m/s can be obtained throughout the altitude range of interest. In addition to the winds, SWIFT will measure ozone densities in the stratosphere. SWIFT has been selected for flight on NASDA's GCOM-A1 satellite and a Phase A study is being supported by ESA and the Canadian Space Agency.
The Stratospheric Wind Interferometer for Transport Studies is a limb viewing satellite instrument which is intended to measure stratospheric wind velocities in the altitude range of 20 to 40 km. Tandem etalon filters made of Germanium and a field-widened Michelson interferometer operating in mid- infrared are major components of this instrument. A He-Ne laser and a CCD camera were used to observe Haidinger and Fizeau fringes in visible light and compare their characteristics with mid-infrared measurements. The Fizeau fringes in the visible can be used to observe the irregularities in the Michelson interferometer's path difference. In addition a CO2 laser operating at 9.26 micrometers has been used to test the Michelson interferometer and the filters together. The filters are thermally tuned to the CO2 laser line and the filter output was incident on a diffuse surface in front of the Michelson input aperture. The Michelson interferometer was then pressure scanned to observe its performance in combination with the filters.
Proof of concept narrow-band etalon filters have been fabricated and characterized for the SWIFT instrument program. The Stratospheric Wind Interferometer For Transport studies is a limb viewing satellite instrument which is intended to measure stratospheric horizontal wind velocities in the altitude range of 20 to 40 km. In addition to providing the atmospheric research community with the first direct measurements of stratospheric dynamics on a global scale, continuous global SWIFT data is expected to improve long range weather forecasting in the troposphere. To isolate the single lines required for the Doppler measurement of the SWIFT instrument, two narrow-band germanium etalon filters centered near 9 micrometer and with 0.8 nm and 2.5 nm bandwidths were fabricated and tested. The SWIFT filter testbed consists of a cryogenic dewar and temperature controller for stabilizing and tuning the filters. The SWIFT filter requirements are discussed, as is the filter testbed design. The measured filter characteristics: transmittance as a function of wavelength, temperature and angle of incidence and tandem filter properties are discussed in the context of satellite instrument requirements.
The Stratospheric Wind Interferometer for Transport Studies (SWIFT) is a satellite-born limb-viewing instrument which will be capable of globally measuring horizontal winds at altitudes of between 20 and 40 km with a precision of < 5 m/s, a vertical resolution of 2 km and a horizontal resolution on the order of a hundred km. SWIFT will map stratospheric dynamics. The data from the instrument will be important input for models which seek to predict the global distribution of stratospheric ozone. In addition, the SWIFT data will provide observational input to tropospheric weather models, which are currently being extended to the stratosphere. With global stratospheric wind data, these enhanced models have the potential to significantly improve weather forecasting in the troposphere. The instrument will observe a thermal emission line of an abundant atmospheric constituent near 8 micrometers using a field widened Michelson interferometer. A doppler shift of the emission line is detected as a phase shift at the output of the interferometer. A 2D array detector monitors the phase both perpendicular to and along the limb, thus mapping the velocity field. The fundamental feasibility of the instrument will be shown. The basic instrument requirements are described and the instrument parameters are derived from them. The instrument will utilize radiatively cooled optics and Stirling cycle coolers for the detector and filters. This instrument will be suitable for inclusion on a medium to large satellite with multiple instruments. The lack of cryogens is consistent with its intended use on the operational weather satellites of the future.