W. David Miller

Interstellar pickup H+ Ions at 8.3 AU: Pioneer 10 plasma and magnetic field analyses

Analysis of Pioneer 10 plasma and magnetic field observations at 8.3 AU in 1975 provides new evidence for the presence of interstellar pickup hydrogen (H + ) ions. Use of plasma sensors that look far from the solar wind direction confirms the spherical shell distribution of the pickup ions in velocity space. Phase space density and flux estimates are closely consistent with those from Ulysses measured under similar conditions. Power spectral analyses of the magnetic field data show a distinct signal a little above the proton gyrofrequency, consistent with the presence of Doppler-shifted ion-cyclotron waves generated by H + pickup ions. These results show that the Pioneer data set has the potential for systematic studies of the global properties of interstellar pickup ions.

Retrieval of Substrate Bearing Strength from Hyperspectral Imagery during the Virginia Coast Reserve (VCR’07) 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).

Variable climatic conditions dominate recent phytoplankton dynamics in Chesapeake Bay

Variable climatic conditions strongly influence phytoplankton dynamics in estuaries globally. Our study area is Chesapeake Bay, a highly productive ecosystem providing natural resources, transportation, and recreation for nearly 16 million people inhabiting a 165,000-km2 watershed. Since World War II, nutrient over-enrichment has led to multiple ecosystem impairments caused by increased phytoplankton biomass as chlorophyll-a (chl-a). Doubled nitrogen (N) loadings from 1945–1980 led to increased chl-a, reduced water clarity, and low dissolved oxygen (DO), while decreased N loadings from 1981–2012 suggest modest improvement. The recent 30+ years are characterized by high inter-annual variability of chl-a, coinciding with irregular dry and wet periods, complicating the detection of long-term trends. Here, we synthesize time-series data for historical and recent N loadings (TN, NO2 + NO3), chl-a, floral composition, and net primary productivity (NPP) to distinguish secular changes caused by nutrient over-enrichment from spatio-temporal variability imposed by climatic conditions. Wet years showed higher chl-a, higher diatom abundance, and increased NPP, while dry years showed lower chl-a, lower diatom abundance, and decreased NPP. Our findings support a conceptual model wherein variable climatic conditions dominate recent phytoplankton dynamics against a backdrop of nutrient over-enrichment, emphasizing the need to separate these effects to gauge progress toward improving water quality in estuaries.

Voyager 2 High Energy Ions Near the Outward Moving Termination Shock

We present results on the recurrence of High Energy Ions (HEIs) in the V2 data about 90 days after the initial sunward‐moving termination shock (TS) crossings of V2 in Aug.–Sept. 2007. We associate the HEIs in Nov.–Dec. 2007 with the outward motion of the TS or with a ripple in the TS so that the TS is again near V2. Comparisons of the timings of the recurrence of the HEI detections and the simultaneous V2 convective plasma, energetic particle, and magnetic field data indicate that the variations in all these V2 data sets are consistent with the TS re‐approach to V2 in Nov.–Dec. 2007. We use our three‐dimensional (3D) kinematic HAFSS model to investigate whether the timing of the arrival at V2 of the increase in solar wind dynamic pressure associated with the December 2006 solar events could have been responsible for the dynamic pressure pulse that moved the TS outward toward V2 ∼90 days after the initial TS crossings of V2. This explanation or, alternatively, a 3D solar wind inhomogeneity‐caused TS rippl...

Interpretation of Absorption Bands in Airborne Hyperspectral Radiance Data

It is demonstrated that hyperspectral imagery can be used, without atmospheric correction, to determine the presence of accessory phytoplankton pigments in coastal waters using derivative techniques. However, care must be taken not to confuse other absorptions for those caused by the presence of pigments. Atmospheric correction, usually the first step to making products from hyperspectral data, may not completely remove Fraunhofer lines and atmospheric absorption bands and these absorptions may interfere with identification of phytoplankton accessory pigments. Furthermore, the ability to resolve absorption bands depends on the spectral resolution of the spectrometer, which for a fixed spectral range also determines the number of observed bands. Based on this information, a study was undertaken to determine under what circumstances a hyperspectral sensor may determine the presence of pigments. As part of the study a hyperspectral imager was used to take high spectral resolution data over two different water masses. In order to avoid the problems associated with atmospheric correction this data was analyzed as radiance data without atmospheric correction. Here, the purpose was to identify spectral regions that might be diagnostic for photosynthetic pigments. Two well proven techniques were used to aid in absorption band recognition, the continuum removal of the spectra and the fourth derivative. The findings in this study suggest that interpretation of absorption bands in remote sensing data, whether atmospherically corrected or not, have to be carefully reviewed when they are interpreted in terms of photosynthetic pigments.

Airborne system for multispectral, multiangle polarimetric imaging

In this paper, we describe the design, fabrication, calibration, and deployment of an airborne multispectral polarimetric imager. The motivation for the development of this instrument was to explore its ability to provide information about water constituents, such as particle size and type. The instrument is based on four 16 MP cameras and uses wire grid polarizers (aligned at 0°, 45°, 90°, and 135°) to provide the separation of the polarization states. A five-position filter wheel provides for four narrow-band spectral filters (435, 550, 625, and 750 nm) and one blocked position for dark-level measurements. When flown, the instrument is mounted on a programmable stage that provides control of the view angles. View angles that range to ±65° from the nadir have been used. Data processing provides a measure of the polarimetric signature as a function of both the view zenith and view azimuth angles. As a validation of our initial results, we compare our measurements, over water, with the output of a Monte Carlo code, both of which show neutral points off the principle plane. The locations of the calculated and measured neutral points are compared. The random error level in the measured degree of linear polarization (8% at 435) is shown to be better than 0.25%.

Shock Waves in Space Environments

We present results on two topics: a) The three‐dimensional (3D) Hybrid Heliospheric Modeling System with Pickup Ions (HHMS‐PI) simulations of shock waves and initial comparisons with ACE and Ulysses data for the Halloween 2003 solar events, including the Ulysses SWICS pickup proton densities; and b) Our analyses of Voyager 2 (V2) data near the termination shock (TS). Previously, we used our time‐dependent 3D Hybrid Heliospheric Modeling System (HHMS) for magnetohydrodynamic (MHD) simulations of transient events originating on the Sun. We now have added the physics of “pickup” proton processes to these models. Interstellar neutral hydrogen flows into the heliosphere and becomes ionized by photoionization and by charge exchange with solar wind protons. These “pickup” protons cause a slowing and heating of the solar wind flow in the outer heliosphere. Both HHMS‐PI and HHMS use continuous solar inputs to simulate processes that originate at the Sun. Our V2 analyses identified some elevated readings in the pla...