We attempted a method of fusing a coarse resolution hyperspectral image and a high spatial resolution image with a few spectral bands to produce a high resolution hyperspectral image, and to extract the spectra of the end-members. The method is based on the linear spectral mixing model and an iterative maximum-likelihood algorithm is used to invert the mixing equation. The effects of noise and misregistration error are investigated. Misregistration seems to be a main factor determining the accuracy of the final products.
The Hyperion instrument on-board the EO1 satellite is an imaging spectrometer capable of acquiring hyperspectral data with over 200 contiguous spectral bands of about 10 nm bandwidth. The instrument is not designed for ocean observation. Nevertheless, case 2 water near the coastal regions with high sediment loading usually has higher reflectance in the visible wavelength region than the clear case 1 water in the open oceans. Hence, the signal-to-noise ratio of Hyperion data over coastal waters may be sufficiently high, such that meaningful measurements of the optical properties of the coastal sea waters are possible. We tested the use of Hyperion imagery in retrieving and mapping the distributions of the coastal sea water optical parameters in the Singapore Strait. The Hyperion reflectance spectra were fitted to a coupled sea water reflectance and atmospheric transmission model. The water reflectance corrected for atmospheric effects could be computed from the fitting parameters. This method of inverse modeling by spectral fitting was able to separate the confounding effects due to scattering by suspended sediments and absorption by chlorophyll and dissolved organic matter. Spatial distributions of these three main constituents of coastal waters could be obtained.
This work aims to extract optical parameters of coastal sea water with high sediment and chlorophyll content by fitting reflectance spectra to a model. Sea-truth water sampling campaigns were carried out from Dec 1996 to Dec 1999 in coastal waters around Singapore. In-situ reflectance spectra were acquired using a portable spectro radiometer. Laboratory measurements of the total suspended solid (TSS) and chlorophyll-a (Chl-a) were made from the water samples. The Chl-a concentration ranges from 1 to 90 mg/m3, with an average value of about 10 mg/m3. The three component model for sea water was used to model the reflectance spectra. The model also includes chlorophyll fluorescence and surface reflection due to skylight. Each reflectance spectrum is fitted to the model by finding a set of the fitting parameters that best fits the reflectance curve to the mode. The downhill simplex method is employed as the optimization procedure. The chlorophyll absorption coefficient at 440 nm is retrieved and is found to relate to the measured chl-A concentration by a power law relation.
We are designing an instrument which will perform correlated emission-transmission image
acquisition, but which departs from previous systems by incorporating a low-power x-ray tube and
generator, rather than a radionuclide source, for the transmission image. The system uses an array
of high-purity germanium (HPGe) detectors and detector electronics with energy discrimination
circuitry to separate x-rays (at 100 or 120 kVp) from higher energy gamma rays from the 99mTc
or 123j radiopharmaceutical injected into the patient. The data acquisition electronics have time
constants matching the charge collection time (50 ns) of the HPGe detectors to maximize count-rate
capabilities (up to 1 million cps per detector element), while maintaining adequate energy resolution
(approximately 10% FWHM). Each detector channel has two energy windows for simultaneous
transmission-emission imaging or for dual-energy x-ray studies. A host computer provides system
control as well as data acquisition, data correction, tomographic image reconstruction, image
display, and data analysis.
As a radionuclide imaging system, this instrument will function as a single-slice SPECT
scanner with high-count rate capabilities and excellent energy resolution for imaging short-lived
radionuclides, improved photopeak discrimination and scatter rejection, and simultaneous imaging
of multiple radionuclides. The system also will generate radiographic images in either a
tomographic or projection scanning mode, while dual-energy x-ray CT will provide material specific
imaging. However, the novel and potentially powerful capabilities of this instrument
would derive from its inherent correlation of functional information from SPECT with precise
anatomic information from CT or the material-specific morphologic information from dual-energy
x-ray CT. The simultaneously acquired radiographic images should relieve the deficiencies of poor
statistics and limited spatial resolution commonly associated with SPECT systems. Dual-energy xray
CT also can provide an energy-corrected and anatomically-correlated map of attenuation
coefficients for more accurate quantitation of emission radionuclide data.