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Research Containing: Earth Observation

Hyperspectral Imaging of River Systems

by on 9 June 2015in Earth Science and Remote Sensing No comment

The Navy has a requirement to rapidly and covertly characterize the coastal environment in support of Joint Strike Initiatives. Over the past 15 years we have demonstrated that spaceborne hyperspectral remote sensing is the best approach to covertly acquire data on shallow water bathymetry, bottom types, hazards to navigation, water clarity and beach and shore trafficability to meet those requirements. The long term goal of this work is to put a hyperspectral imager capable of making the appropriate measurements in space to demonstrate this capability.

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Hyperspectral imaging of rivers and estuaries

by on 9 June 2015in Earth Science and Remote Sensing No comment

The Hyperspectral Imager for the Coastal Ocean (HICO) is the first spaceborne imaging spectrometer designed to sample the coastal ocean. HICO samples selected coastal regions at 92 m ground sample distance with full spectral coverage (88 channels covering 400 to 900 nm) and a high signal-to-noise ratio to resolve the complexity of the coastal ocean. HICO has been operating on the International Space Station since October 2009 and collected over 8000 scenes for more than 50 users. We have been using HICO data to study major rivers and estuaries in the US and Asia. Our results show the advantages of HICO’s additional spectral channels and higher spatial resolution for studying these complex coastal waters. We use these data to suggest requirements for spatial and spectral sampling for future ocean color sensors.

Related URLs:
http://dx.doi.org/10.1117/12.2023401

The Nightsat mission concept

by on 9 June 2015in Earth Science and Remote Sensing No comment

Nightsat is a concept for a satellite system capable of global observation of the location, extent and brightness of night‐time lights at a spatial resolution suitable for the delineation of primary features within human settlements. Based on requirements from several fields of scientific inquiry, Nightsat should be capable of producing a complete cloud‐free global map of lights on an annual basis. We have used a combination of high‐resolution field spectra of outdoor lighting, moderate resolution colour photography of cities at night from the International Space Station, and high‐resolution airborne camera imagery acquired at night to define a range of spatial, spectral, and detection limit options for a future Nightsat mission. The primary findings of our study are that Nightsat should collect data from a near‐synchronous orbit in the early evening with 50 to 100 m spatial resolution and have detection limits of 2.5E−8 Watts cm−2sr−1µm−1 or better. Although panchromatic low‐light imaging data would be useful, multispectral low‐light imaging data would provide valuable information on the type or character of lighting; potentially stronger predictors of variables such as ambient population density and economic activity; and valuable information to predict response of other species to artificial night lighting. The Nightsat mission concept is unique in its focus on observing a human activity, in contrast to traditional Earth observing systems that focus on natural systems.

Related URLs:
http://dx.doi.org/10.1080/01431160600981525

Overview and sample applications of SMILES and Odin-SMR retrievals of upper tropospheric humidity and cloud ice mass

by on 9 June 2015in Earth Science and Remote Sensing No comment

Retrievals of cloud ice mass and humidity from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and the Odin-SMR (Sub-Millimetre Radiometer) limb sounder are presented and example applications of the data are given. SMILES data give an unprecedented view of the diurnal variation of cloud ice mass. Mean regional diurnal cycles are reported and compared to some global climate models. Some improvements in the models regarding diurnal timing and relative amplitude were noted, but the models' mean ice mass around 250 hPa is still low compared to the observations. The influence of the ENSO (El Niño–Southern Oscillation) state on the upper troposphere is demonstrated using 12 years of Odin-SMR data. The same retrieval scheme is applied for both sensors, and gives low systematic differences between the two data sets. A special feature of this Bayesian retrieval scheme, of Monte Carlo integration type, is that values are produced for all measurements but for some atmospheric states retrieved values only reflect a priori assumptions. However, this "all-weather" capability allows a direct statistical comparison to model data, in contrast to many other satellite data sets. Another strength of the retrievals is the detailed treatment of "beam filling" that otherwise would cause large systematic biases for these passive cloud ice mass retrievals. The main retrieval inputs are spectra around 635/525 GHz from tangent altitudes below 8/9 km for SMILES/Odin-SMR, respectively. For both sensors, the data cover the upper troposphere between 30° S and 30° N. Humidity is reported as both relative humidity and volume mixing ratio. The vertical coverage of SMILES is restricted to a single layer, while Odin-SMR gives some profiling capability between 300 and 150 hPa. Ice mass is given as the partial ice water path above 260 hPa, but for Odin-SMR ice water content, estimates are also provided. Besides a smaller contrast between most dry and wet cases, the agreement with Aura MLS (Microwave Limb Sounder) humidity data is good. In terms of tropical mean humidity, all three data sets agree within 3.5 %RHi. Mean ice mass is about a factor of 2 lower compared to CloudSat. This deviation is caused by the fact that different particle size distributions are assumed, combined with saturation and a priori influences in the SMILES and Odin-SMR data.

Related URLs:
http://www.atmos-chem-phys.net/14/12613/2014/
http://www.atmos-chem-phys.net/14/12613/2014/acp-14-12613-2014.pdf

Vicarious calibrations of HICO data acquired from the International Space Station

by on 9 June 2015in Earth Science and Remote Sensing No comment

The Hyperspectral Imager for the Coastal Ocean (HICO) presently onboard the International Space Station (ISS) is an imaging spectrometer designed for remote sensing of coastal waters. The instrument is not equipped with any onboard spectral and radiometric calibration devices. Here we describe vicarious calibration techniques that have been used in converting the HICO raw digital numbers to calibrated radiances. The spectral calibration is based on matching atmospheric water vapor and oxygen absorption bands and extraterrestrial solar lines. The radiometric calibration is based on comparisons between HICO and the EOS/MODIS data measured over homogeneous desert areas and on spectral reflectance properties of coral reefs and water clouds. Improvements to the present vicarious calibration techniques are possible as we gain more in-depth understanding of the HICO laboratory calibration data and the ISS HICO data in the future.

Related URLs:
http://ao.osa.org/abstract.cfm?URI=ao-51-14-2559

How Earth remote sensing from the International Space Station complements current satellite‐based sensors

by on 9 June 2015in Earth Science and Remote Sensing No comment

The International Space Station (ISS) will provide an Earth‐ and space‐observing platform that will support sensors built by 16 different countries and deliver data and images for local, regional and global research. When complete, it will be an exceptional platform for conducting remote sensing of the Earth, astrophysics, and space physics research programmes. Additionally, the ISS will operate as a testbed for engineering studies and complex technological developments that will benefit future Earth‐observing capabilities. The key question addressed here is: What can the ISS give the Earth Science community that current and planned satellite platforms do not already offer? To answer this query we provide characteristics of the ISS structure, current and proposed instruments, orbital characteristics, and instrument accessibility by crew. We show how the Earth‐observing instruments on ISS complement current satellite‐based Earth‐observing sensors.

Related URLs:
http://dx.doi.org/10.1080/01431160600552250

International Space Station Agricultural Camera (ISSAC) Sensor Onboard the International Space Station (ISS) and Its Potential Use on the Earth Observation

by on 9 June 2015in Earth Science and Remote Sensing No comment

Recently launched and installed inside the Window Observational Research Facility (WORF) in the International Space Station (ISS), the International Space Station Agricultural Camera (ISSAC) sensor is an area-scan multi-spectral optical imaging system built by students and faculty at the University of North Dakota (UND). Radiometric calibration was conducted before launch and performance validation was evaluated with radiance extracted from Landsat5 TM image that was overpassed nearly at the same time as ISSAC overpass. Ground truth measurement with Analytical Spectral Devices (ASD, ASD Inc., Boulder CO) was also carried out over fairly homogenous regions of interest such as bare soil, gravel parking lot, crop and short grass pastures. Using the 6S radiative transfer model, radiances measured at the top-of-the atmosphere were converted into surface reflectance. Atmospheric corrected surface reflectance from ISSAC images was compared with the spectrum of ground ASD measurement. The results for both radiance and surface reflectance show fairly good agreements. This indicates that ISSAC would be a prospective candidate that would be able to fill the temporal gaps of Landsat 16-day revisit cycle. Higher rate of temporal opportunities from ISSAC sensor will result in significant improvement on decision making for users especially in time sensitive disaster management, farming practices or environmental issues occurred in short time frame.

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Comparison of ozone profiles between Superconducting Submillimeter-Wave Limb-Emission Sounder and worldwide ozonesonde measurements

by on 9 June 2015in Earth Science and Remote Sensing No comment

We compared ozone profiles measured by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) with those taken at worldwide ozonesonde stations. To assess the quality of the SMILES version 2.3 ozone data for 16–30 km, 601 ozonesonde profiles were compared with the coincident SMILES ozone profiles. The agreement between SMILES and ozonesonde measurements was generally good within 5%–7% for 18–30 km at middle and high latitudes but degraded below 18 km. At low latitudes, however, the SMILES ozone data showed larger values (~6%–15% for 20–26 km) than those at middle and high latitudes. To explain this bias, we explored some possible issues in the ozonesonde measurement system. One possibility is due to a pressure bias in radiosonde measurements with a pressure sensor, but it would be within a few percent. We also examined an issue of the ozonesonde's response time. The response time was estimated from ozonesonde measurements with ascending and descending profiles showing clear difference, by using the time lag correction method to minimize the difference between them. Our estimation shows 28 s on average which is a similar value derived by prelaunch preparation. By applying this correction to the original profiles, we found a negative bias of the ascending ozonesonde measurement more than 7% at 20 km in the equatorial latitude where the vertical gradient of ozone is steep. The corrected ozonesonde profiles showed better agreement with the SMILES data. We suggest that the response time of ozonesondes could create a negative bias, particularly in the lower stratosphere at equatorial latitudes.

Related URLs:
http://dx.doi.org/10.1002/2013JD021094
http://onlinelibrary.wiley.com/doi/10.1002/2013JD021094/abstract

Validation of ozone data from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)

by on 9 June 2015in Earth Science and Remote Sensing No comment

The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station provided global measurements of ozone profiles in the middle atmosphere from 12 October 2009 to 21 April 2010. We present validation studies of the SMILES version 2.1 ozone product based on coincidence statistics with satellite observations and outputs of chemistry and transport models (CTMs). Comparisons of the stratospheric ozone with correlative data show agreements that are generally within 10%. In the mesosphere, the agreement is also good and better than 30% even at a high altitude of 73 km, and the SMILES measurements with their local time coverage also capture the diurnal variability very well. The recommended altitude range for scientific use is from 16 to 73 km. We note that the SMILES ozone values for altitude above 26 km are smaller than some of the correlative satellite datasets; conversely the SMILES values in the lower stratosphere tend to be larger than correlative data, particularly in the tropics, with less than 8% difference below ~24 km. The larger values in the lower stratosphere are probably due to departure of retrieval results between two detection bands at altitudes below 28 km; it is ~3% at 24 km and is increasing rapidly down below.

Related URLs:
http://dx.doi.org/10.1002/jgrd.50434
http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50434/abstract