We present an integrated end-end simulation of the spectral images that will be obtained by the weave spectrograph, which aims to include full modelling of all effects from the top of the atmosphere to the detector. These data are based in input spectra from a combination of library spectra and synthetic models, and will be used to provide inputs for an endend test of the full weave data pipeline and archive systems, prior to 1st light of the instrument.
Understanding the Earth spectral bio-signatures provides an important reference datum for accurate de-convolution of
collapsed spectral signals from potential earth-like planets of other star systems. This study presents a new ray tracing
computation method including an improved 3D optical earth model constructed with the coastal line and vegetation
distribution data from the Global Ecological Zone (GEZ) map. Using non-Lambertian bidirectional scattering
distribution function (BSDF) models, the input earth surface model is characterized with three different scattering
properties and their annual variations depending on monthly changes in vegetation distribution, sea ice coverage and
illumination angle. The input atmosphere model consists of one layer with Rayleigh scattering model from the sea level
to 100 km in altitude and its radiative transfer characteristics is computed for four seasons using the SMART codes. The
ocean scattering model is a combination of sun-glint scattering and Lambertian scattering models. The land surface
scattering is defined with the semi empirical parametric kernel method used for MODIS and POLDER missions. These
three component models were integrated into the final Earth model that was then incorporated into the in-house built
integrated ray tracing (IRT) model capable of computing both spectral imaging and radiative transfer performance of a
hypothetical space instrument as it observes the Earth from its designated orbit. The IRT model simulation inputs include
variation in earth orientation, illuminated phases, and seasonal sea ice and vegetation distribution. The trial simulation
runs result in the annual variations in phase dependent disk averaged spectra (DAS) and its associated bio-signatures
such as NDVI. The full computational details are presented together with the resulting annual variation in DAS and its
associated bio-signatures.
The Geostationary Ocean Colour Instrument (GOCI) is a satellite ocean colour instrument on board the
Communication-Ocean-Meteorology Satellite (COMS) scheduled to be launched into a geostationary orbit sometime after
late 2009. GOCI primary science objectives are i) to monitor the marine environments around Korean peninsula, ii) to
produce the fishery information such as chlorophyll concentration and iii) to monitor the long-term and short-term changes
in marine ecosystem. We report a new end-to-end optical model for GOCI in-orbit radiometric and imaging performance
verification. The model includes the source (i.e. the sun), target (i.e. a 2500 km x 2500 km region of the Earth's surface)
and the payload (i.e. GOCI optical system) incorporated in the single optical ray tracing environment. It was then applied
for the measurement simulation for red tide infection commonly observed in the Korean coastal water environment. The
simulation results show that the estimated water leaving radiance (WLR) of 14 red tide-infected case-I water target scenes
exhibits a close proximity to those obtained from the COART model, and satisfies the red tide detection criteria reported
elsewhere. The simulated WLR results were also used to check the validity of 14 chlorophyll algorithms commonly used in
the ocean science field. This demonstrates the practical usefulness of the model, as an important mission-support and
analysis tool. It is also envisaged that the model deployment can bring a significant improvement, in the process throughput,
to the GOCI pre-flight and in-flight performance verification phases. The model concept, simulation results and
implications are described in detail.
Discrepancies between recent global earth albedo anomaly data obtained from the climate models, space and ground
observations call for a new and better earth reflectance measurement technique. The SALEX (Space Ashen Light Explorer)
instrument is a space-based visible and IR instrument for precise estimation of the global earth albedo by measuring the
ashen light reflected off the shadowy side of the Moon from the low earth orbit. The instrument consists of a conventional
2-mirror telescope, a pair of a 3-mirror visible imager and an IR bolometer. The performance of this unique multi-channel
optical system is sensitive to the stray light contamination due to the complex optical train incorporating several reflecting
and refracting elements, associated mounts and the payload mechanical enclosure. This could be further aggravated by the
very bright and extended observation target (i.e. the Moon). In this paper, we report the details of extensive stray light
analysis including ghosts and cross-talks, leading to the optimum set of stray light precautions for the highest
signal-to-noise ratio attainable.
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