James E. Davies

A Survey for Low Surface Brightness Galaxies around M31. I. The Newly Discovered Dwarf Andromeda V

We present B-, V-, and I-band images, as well as an Hα image, of Andromeda VI (And VI). This is the second newly identified dwarf spheroidal (dSph) companion to M31 found using a digital filtering technique applied to the second Palomar Sky Survey for which about 1550 deg2 now have been surveyed. And VI was confirmed to be a nearby dSph galaxy when it resolved into stars easily with a short V-band exposure with the 4 m telescope. Subarcsecond images taken at the Kitt Peak WIYN 3.5 m telescope provided (I, V-I) and (V, B-V) color-magnitude diagrams that yield a distance of 775 ± 35 kpc using the tip of the red giant branch method, and a mean metallicity of [Fe/H] = -1.58 ± 0.20 with a dispersion of approximately 0.3 dex. And VI has a galactocentric distance of roughly 271 kpc and MV = -11.3. All observed properties of And VI are consistent with its classification as a dSph companion to M31. Despite the recent identification of the And V, And VI, and Cas dwarfs, the Local Group luminosity function remains highly deficient in faint galaxies relative both to CDM simulations of its formation, and to the luminosity functions for richer clusters of galaxies.

Daily MODIS 500 m reflectance anisotropy direct broadcast DB products for monitoring vegetation phenology dynamics

Land surface vegetation phenology is an efficient bio-indicator for monitoring ecosystem variation in response to changes in climatic factors. The primary objective of the current article is to examine the utility of the daily MODIS 500 m reflectance anisotropy direct broadcast (DB) product for monitoring the evolution of vegetation phenological trends over selected crop, orchard, and forest regions. Although numerous model-fitted satellite data have been widely used to assess the spatio-temporal distribution of land surface phenological patterns to understand phenological process and phenomena, current efforts to investigate the details of phenological trends, especially for natural phenological variations that occur on short time scales, are less well served by remote sensing challenges and lack of anisotropy correction in satellite data sources. The daily MODIS 500 m reflectance anisotropy product is employed to retrieve daily vegetation indices (VI) of a 1 year period for an almond orchard in California and for a winter wheat field in northeast China, as well as a 2 year period for a deciduous forest region in New Hampshire, USA. Compared with the ground records from these regions, the VI trajectories derived from the cloud-free and atmospherically corrected MODIS Nadir BRDF (bidirectional reflectance distribution function) adjusted reflectance (NBAR) capture not only the detailed footprint and principal attributes of the phenological events (such as flowering and blooming) but also the substantial inter-annual variability. This study demonstrates the utility of the daily 500 m MODIS reflectance anisotropy DB product to provide daily VI for monitoring and detecting changes of the natural vegetation phenology as exemplified by study regions comprising winter wheat, almond trees, and deciduous forest.

Numerical experiments in atmospheric scintillation correlation for applications in dual channel optical communications

A method for reducing noise in near-IR laser communications has been proposed that relies upon the dual wavelength output of the He-Xe laser having a high level of noise coherence. However, in transmissions through the atmospheric boundary layer, an additional and significant noise component is added by atmospheric scintillation. These scintillations are mainly limited to frequencies of less than 1 kHz and are correlated in the two laser channels to a degree determined by the channel wavelength separation, the transmission range and the severity of the turbulence regime. To analyze the propagation of waves in random media one normally considers the statistics of the field. In the case of small angle forward scattering, which is the case of interest in laser propagation, field moments higher than the fourth are so difficult to solve that no solutions are known outside of the asymptotic weak and strong approximations. An alternative approach is to conduct numerical experiments in which one generates a realization of the random medium (with the desired statistics) and then calculates the wave field. We have numerically modeled the spatial irradiance intensity as a function of range from a point source under turbulence regimes typical of daytime conditions near the Earth’s surface. Simulations were performed for two closely separated channels in the near-IR (1556.5 and 1558.1 nm). We present the results of these simulations together with the implications for the mitigation of atmospheric scintillation noise by common mode rejection.

A Survey for Low Surface Brightness Dwarf Galaxies Around M31

By applying a digital filtering technique to 1550 square degrees of the POSS-II in the vicinity of M31, we found two previously unidentified very low surface brightness dwarf galaxies which we designate And V and VI. Follow-up imaging with the KPNO 4-m telescope resolved these into stars easily. The V- and I- band images of And V indicate a distance similar to that of M31, and approximately -1.5. All evidence strongly supports its classification as a dwarf spheroidal companion to M31. Data for And VI are being analyzed, but preliminary indications support a similar conclusion. Our search for more dwarfs, including follow-up observations of numerous candidates found via digital filtering, is incomplete; thus, further identifications may be forthcoming.

Community Satellite Processing Package from Direct Broadcast: Providing real-time Satellite Data to every corner of the world

Space Science and Engineering Center (SSEC) and its Cooperative Institute for Meteorological Satellite Studies (CIMSS) have supported the international Direct Broadcast/Readout (DB/DR) user community since 1985 through the distribution of the International TOVS and ATOVS Processing Packages (ITPP, IAPP) for NOAA Polar Orbiting Environmental Satellite (POES), and since 2000 via the International MODIS/AIRS Processing Package (IMAPP) for NASA Terra and Aqua. Since 2007, SSEC/CIMSS has also participated in the development of regional versions of software for generating Cross-Track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) Sensor Data Records (SDRs), and for Visible Infrared Imaging Radiometer Suite (VIIRS) atmosphere and cloud Environmental Data Records (EDRs). Currently SSEC/CIMSS is supported by the NOAA JPSS program scientist and NASA to continue facilitating the use of polar orbiter satellite data through the initial development of a newly conceived Community Satellite Processing Package (CSPP) that will support the Suomi-NPP/JPSS and, subsequently, build up over time to support GOES-R with CSPP Geosynchronous Earth Orbit (GEO) component, as well as other international polar orbiting and geostationary meteorological and environmental satellites and their regional user communities.

Modification of SeaDAS SWIR atmospheric correction scheme for accurate retrieval of NIR remote sensing reflectance in the river delta regions of the world

Coastal waters in the vicinity of the river delta regions of the world are characterized by significant concentrations of suspended sediments. To estimate the water sediment load from satellite observations, an important step is to accurately remove the optical effects of the intervening atmosphere. The NASA SeaDAS code [1] has been shown to accurately correct MODIS satellite data for atmospheric effects over most aquatic regimes, using near infrared (NIR) bands where water turbidity is low, and shortwave infrared (SWIR) bands where the NIR bands indicate high turbidity [2]. However, at very high sediment loads, of circa 500 g/m3 and above - and this is not an unusually high level in delta regions - the SWIR bands can themselves be influenced by the suspended sediment and their utility for atmospheric correction thus compromised. Indeed, the ocean color NIR bands saturate under these conditions and so become unviable for any manner of atmospheric correction. We have employed the MODIS water vapor bands in the 900 nm region of the spectrum to provide a correction to the 1.24 µm band MODIS reflectance, thereby extending the utility of the SeaDAS SWIR atmospheric correction to very high sediment concentration waters.

AIRS Single Field of View Cloud Detection and Cloud Property Retrieval

A great need exists amongst X-band direct broadcast regional users for near real-time, high spatial resolution cloud detection and cloud property retrieval to support regional interdisciplinary applications. As part of the International MODIS and AIRS Processing Package (IMAPP), the objective treatment of spatial and spectral information, including principal component and residual techniques, is provided by the AIRS single field of view clear and cloud detection and cloud property retrieval algorithm. This algorithm, known as Minimum Local Emissivity Variance (MLEV), is used to retrieve both cloud height and cloud spectral emissivity. The ECMWF model analysis is used to demonstrate that high quality clear radiances can improve the yield and quality of cloud spectral emissivity and height, quantities that are precursors to retrieving cloud micro-physical properties and cloudy sounding profiles. In this paper we describe in detail the procedure employed to achieve this goal. The use of cloud spectral emissivity and height in retrieving cloud micro-physical properties is discussed together with their utility in identifying cloud contaminated soundings in the IMAPP AIRS only single field of view retrieval.

Atmospheric correction of satellite observations of ocean color with the Navy aerosol model

Atmospheric correction of ocean colour is routinely achieved by fitting radiometric observations at near near-infrared wavelengths to radiances predicted for a range of aerosol types. The best-fitting candidate aerosol model can then be used to compute radiances in the visible part of the spectrum, enabling an atmospheric correction to be applied there. The Navy Aerosol Model (NAM) is a multi-component aerosol model which may be suitable for this purpose. The components of NAM are closely tied to the physical processes which generate them and this allows for some expectation on the spatial homogeneity of the component optical depths. Presented is an atmospheric correction scheme based upon NAM and implemented for SeaWiFS. Some conclusions are drawn about the efficacy of extrapolating to visible wavelengths those estimates of aerosol type and amount made at near-infrared wavelengths.