Very Shallow Water Bathymetry Retrieval from Hyperspectral Imagery at the Virginia Coast Reserve (VCR\u2707) Multi-Sensor Campaign

A number of institutions, including the Naval Research Laboratory (NRL), have developed look up tables for remote retrieval of bathymetry and in-water optical properties from hyperspectral imagery (HSI) [6]. For bathymetry retrieval, the lower limit is the very shallow water case (here defined as \u3c 2m), a depth zone which is not well resolved by many existing bathymetric LIDAR sensors, such as SHOALS [4]. The ability to rapidly model these shallow water depths from HSI directly has potential benefits for combined HSI/LIDAR systems such as the Compact Hydrographic Airborne Rapid Total Survey (CHARTS) [10]. In this study, we focused on the validation of a near infra-red feature, corresponding to a local minimum in absorption (and therefore a local peak in reflectance), which can be correlated directly to bathymetry with a high degree of confidence. Compared to other VNIR wavelengths, this particular near-IR feature corresponds to a peak in the correlation with depth in this very shallow water regime, and this is a spectral range where reflectance depends primarily on water depth (water absorption) and bottom type, with suspended constituents playing a secondary role

Parker Solar Probe Imaging of the Night Side of Venus

We present images of Venus from the Wide-Field Imager for Parker Solar Probe (WISPR) telescope on board the Parker Solar Probe (PSP) spacecraft, obtained during PSP's third and fourth flybys of Venus on 2020 July 11 and 2021 February 20, respectively. Thermal emission from the surface is observed on the night side, representing the shortest wavelength observations of this emission ever, the first detection of the Venusian surface by an optical telescope observing below 0.8 μm. Consistent with previous observations at 1 μm, the cooler highland areas are fainter than the surrounding lowlands. The irradiances measured by WISPR are consistent with model predictions assuming a surface temperature of T = 735 K. In addition to the thermal emission, the WISPR images also show bright nightglow emission at the limb, and we compare the WISPR intensities with previous spectroscopic measurements of the molecular oxygen nightglow lines from Venus Express

Linking goniometer measurements to hyperspectral and multi-sensor imagery for retrieval of beach properties and coastal characterization

In June 2011, a multi-sensor airborne remote sensing campaign was flown at the Virginia Coast Reserve Long Term Ecological Research site with coordinated ground and water calibration and validation (cal/val) measurements. Remote sensing imagery acquired during the ten day exercise included hyperspectral imagery (CASI-1500), topographic LiDAR, and thermal infra-red imagery, all simultaneously from the same aircraft. Airborne synthetic aperture radar (SAR) data acquisition for a smaller subset of sites occurred in September 2011 (VCR\u2711). Focus areas for VCR\u2711 were properties of beaches and tidal flats and barrier island vegetation and, in the water column, shallow water bathymetry. On land, cal/val emphasized tidal flat and beach grain size distributions, density, moisture content, and other geotechnical properties such as shear and bearing strength (dynamic deflection modulus), which were related to hyperspectral BRDF measurements taken with the new NRL Goniometer for Outdoor Portable Hyperspectral Earth Reflectance (GOPHER). This builds on our earlier work at this site in 2007 related to beach properties and shallow water bathymetry. A priority for VCR\u2711 was to collect and model relationships between hyperspectral imagery, acquired from the aircraft at a variety of different phase angles, and geotechnical properties of beaches and tidal flats. One aspect of this effort was a demonstration that sand density differences are observable and consistent in reflectance spectra from GOPHER data, in CASI hyperspectral imagery, as well as in hyperspectral goniometer measurements conducted in our laboratory after VCR\u2711

Hyperspectral Imager for the Coastal Ocean: instrument description and first images

The Hyperspectral Imager for the Coastal Ocean (HICO) is the first spaceborne hyperspectral sensor designed specifically for the coastal ocean and estuarial, riverine, or other shallow-water areas. The HICO generates hyperspectral images, primarily over the 400–900nm spectral range, with a ground sample distance of ≈90m (at nadir) and a high signal-to-noise ratio. The HICO is now operating on the International Space Station (ISS). Its cross-track and along-track fields of view are 42km (at nadir) and 192 km, respectively, for a total scene area of 8000km². The HICO is an innovative prototype sensor that builds on extensive experience with airborne sensors and makes extensive use of commercial off-theshelf components to build a space sensor at a small fraction of the usual cost and time. Here we describe the instrument’s design and characterization and present early images from the ISS.This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. The paper can be found atthe following URL on the OSA website: http://www.opticsinfobase.org/ao/home.cfm. Systematic ormultiple reproduction or distribution to multiple locations viaelectronic or other means is prohibited and is subject to penaltiesunder law

The Second SIMBIOS Radiometric Intercomparison (SIMRIC-2), March-November 2002

The second SIMBIOS (Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies) Radiometric Intercomparison (SIMRIC-2) was carried out in 2002. The purpose of the SIMRIC's was to ensure a common radiometric scale among the calibration facilities that are engaged in calibrating in-situ radiometrics used for ocean color-related research and to document the calibration procedures and protocols. The SeaWIFS Transfer Radiometer (SXR-II) measured the calibration radiances at six wavelengths from 411nm to 777nm in the ten laboratories participating in the SIMRIC-2. The measured radiances were compared with the radiances expected by the laboratories. The agreement was within the combined uncertainties for all but two laboratories. Likely error sources were identified in these laboratories and corrective measures were implemented. NIST calibrations in December 2001 and January 2003 showed changes ranging from -0.6% to +0.7% for the six SXR-II channels. Two independent light sources were used to monitor changes in the SXR-II responsivity between the NIST calibrations. A 2% variation of the responsivity of channel 1 of the SXR-II was detected, and the SXR-II responsivity was corrected using the monitoring data. This report also compared directional reflectance calibrations of a Spectralon plaque by different calibration facilitie

Hyperspectral Imager Calibration in the Blue: Issues and Experiments

The United States Naval Research Laboratory (NRL) has conducted hyperspectral remote sensing of the coastal ocean environment for nearly two decades, employing sensors that span the wavelength range from the near ultraviolet through the short wave infrared. Of these, four operate in the visible to near infrared (VNIR), including three used on airborne platforms: the Portable Hyperspectral Imager for Low Light Spectroscopy (PHILLS), a commercial CASI-1500, the UAV capable micro-Small Hyperspectral Imager for the Naval Environment (microSHINE), and one aboard the International Space Station (ISS)- the Hyperspectral Imager for the Coastal Ocean (HICO). It is interesting to note that all four sensors have shown field radiances that are lower than expected at the shortest wavelength up to approximately 450-500nm, depending on the sensor. This necessitates the use of an empirical scaling at these wavelengths. There is also some evidence that hyperspectral imagers used by other groups have a similar issue. Suspected causes include atmospheric correction or calibration. This poster discusses sensor calibration and measurements taken at NRL at ground level (i.e. little atmosphere contribution) that seem to indicate that calibration does contribute to the problem of low radiances at the blue end of the spectrum. The NRL sensors were calibrated using NIST traceable integrating spheres, one using only QTH lamps operating at about 3000K, and another blue-enhanced sphere equipped with a 300W Xe arc lamp in addition to QTH lamps. It should be noted that the first sphere was included in the first SIMBIOS Radiometric Intercomparison (SIMRIC) in 2001 and was shown to be within 2% agreement of the SeaWiFS Transfer Radiometer SXR-II at all wavelengths. In addition, the calibration of this sphere is checked using commercial Field Spec Pro and 3 spectrometers with current calibrations and it is consistently within a few percent agreement at all wavelengths. The calibration spheres themselves are not the problem. It is more likely that the problem is related to the difference between the blue-deficient spectrum used to calibrate the sensors and the blue-rich spectra measured in the field. Almost all of these sensors are calibrated using an integrating sphere illuminated by quartz halogen QTH sources that operate at a color temperature of about 3000k. These sources have a very low output at the problematic blue wavelengths and a relatively much larger output at the red and infrared wavelengths. This is exactly opposite of what is measured in the field. In this case, the problem with calibration could be related to stray light or linearity issues in the sensor. This poster will discuss the investigations into resolving this issue. For instance, it appears that stray light may not be the issue as demonstrated during the calibration of HICO. At that time, HICO was placed in front of the QTH only sphere and the blue-enhanced sphere, which have very different spectral shapes. Both yielded almost the exact same calibration coefficients at all wavelengths and still the on-orbit radiances required an empirical correction in the blue

Comparison of spectral radiance calibrations at oceanographic and atmospheric research laboratories

International audienc

Bathymetry Retrieval from Hyperspectral Imagery in the Very Shallow Water Limit: a Case Study from the 2007 Virginia Coast Reserve (VCR\u2707) Multi-Sensor Campaign

We focus on the validation of a simplified approach to bathymetry retrieval from hyperspectral imagery (HSI) in the very shallow water limit (less than 1–2 m), where many existing bathymetric LIDAR sensors perform poorly. In this depth regime, near infra-red (NIR) reflectance depends primarily on water depth (water absorption) and bottom type, with suspended constituents playing a secondary role. Our processing framework exploits two optimal regions where a simple model depending on bottom type and water depth can be applied in the very shallow limit. These two optimal spectral regions are at a local maximum in the near infra-red reflectance near 810 nm, corresponding to a local minimum in absorption, and a maximum in the first derivative of the reflectance near 720 nm. These two regions correspond to peaks in spectral correlation with bathymetry at these depths

Retrieval of Substrate Bearing Strength from Hyperspectral Imagery during the Virginia Coast Reserve (VCR\u2707) Multi-Sensor Campaign

Hyperspectral imagery (HSI) derived from remote sensing can delineate surface properties of substrates such as type, moisture, and grain size. These are critical parameters that determine the substrate bearing strength. Although HSI only sees the surface layer, statistics can be derived that relate surface properties to the likely bearing strength of soils in particular regions. This information can be used to provide an initial map estimate on large scales of potential bearing strength. We describe an initial validation study at the Virginia Coast Reserve relating airborne HSI to in situ spectral and geotechnical measurements through a spectral-geotechnical lookup table (LUT)