Santo V. Salinas

No oceans on Titan from the absence of a near-infrared specular reflection

With its substantial atmosphere of nitrogen, hydrocarbons and nitriles, Saturns moon Titan is a unique planetary satellite. Photochemical processing of the gaseous constituents produces an extended haze that obscures the surface. Soon after the Voyager fly-bys in 1980 and 1981 photochemical models led to the conclusion that there should be enough liquid methane/ethane/nitrogen to cover the surface to a depth of several hundred metres. Recent Earth-based radar echoes imply that surface liquid may be present at a significant fraction of the locations sampled. Here we present ground-based observations (at near-infrared wavelengths) and calculations showing that there is no evidence thus far for surface liquid. Combined with the specular signatures from radar observations, we infer mechanisms that produce very flat solid surfaces, involving a substance that was liquid in the past but is not in liquid form at the locations we studied.

Multiparameter retrieval of water optical properties from above-water remote-sensing reflectance using the simulated annealing algorithm.

Water-leaving radiance, measured just above the ocean surface, contains important information about near-surface or subsurface processes that occur on or below the deep ocean and coastal water. As such, retrieving seawater inherent optical properties (IOPs) is an important step to determining water type, subsurface light field, turbidity, pigment concentration, and sediment loading. However, the retrieval (or inversion) of seawater IOPs from just above water radiance measurements is a multiparameter nonlinear problem that is difficult to solve by conventional optimization methods. The applicability of the simulated annealing algorithm (SA) is explored as a nonlinear global optimizer to solve this multiparameter retrieval problem. The SA algorithm is combined with widely known semianalytical relations for seawaters IOPs to parameter invert these properties from simulated and measured water-leaving reflectance spectra. Furthermore, given the versatility of the SA algorithm, the scheme is extended to retrieve water depth from input reflectance data. Extensive tests and comparisons with in situ and simulated data sets compiled by the International Ocean-Color Coordinating Group are presented. Field data include reflectance spectra acquired with a handheld GER 1500 spectroradiometer and absorption measurements, performed with the AC-9 instrument on waters around Singapores nearby islands.

Daytime Top-of-the-Atmosphere Cirrus Cloud Radiative Forcing Properties at Singapore

AbstractDaytime top-of-the-atmosphere (TOA) cirrus cloud radiative forcing (CRF) is estimated for cirrus clouds observed in ground-based lidar observations at Singapore in 2010 and 2011. Estimates are derived both over land and water to simulate conditions over the broader Maritime Continent archipelago of Southeast Asia. Based on bookend constraints of the lidar extinction-to-backscatter ratio (20 and 30 sr), used to solve extinction and initialize corresponding radiative transfer model simulations, relative daytime TOA CRF is estimated at 2.858–3.370 W m−2 in 2010 (both 20 and 30 sr, respectively) and 3.078–3.329 W m−2 in 2011 and over water between −0.094 and 0.541 W m−2 in 2010 and −0.598 and 0.433 W m−2 in 2011 (both 30 and 20 sr, respectively). After normalizing these estimates for an approximately 80% local satellite-estimated cirrus cloud occurrence rate, they reduce in absolute daytime terms to 2.198–2.592 W m−2 in 2010 and 2.368–2.561 W m−2 in 2011 over land and −0.072–0.416 W m−2 in 2010 and −0...

Applying Advanced Ground-Based Remote Sensing in the Southeast Asian Maritime Continent to Characterize Regional Proficiencies in Smoke Transport Modeling

ABSTRACTThis work describes some of the most extensive ground-based observations of the aerosol profile collected in Southeast Asia to date, highlighting the challenges in simulating these observations with a mesoscale perspective. An 84-h WRF Model coupled with chemistry (WRF-Chem) mesoscale simulation of smoke particle transport at Kuching, Malaysia, in the southern Maritime Continent of Southeast Asia is evaluated relative to a unique collection of continuous ground-based lidar, sun photometer, and 4-h radiosonde profiling. The period was marked by relatively dry conditions, allowing smoke layers transported to the site unperturbed by wet deposition to be common regionally. The model depiction is reasonable overall. Core thermodynamics, including land/sea-breeze structure, are well resolved. Total model smoke extinction and, by proxy, mass concentration are low relative to observation. Smoke emissions source products are likely low because of undersampling of fires in infrared sun-synchronous satellite...

Quick analysis of wave patterns generated by tsunami waves and captured by SPOT imagery

Following the devastating Earthquake off the west coast for northern Sumatra on December 26th 2004, a series of tsunami waves were generated from the initial shock and following after–shocks as was reported by several seismic stations around the world. Satellite images of the affected regions has shown the devastating effects of these traveling waves when interacting with beaches and regions of low depth. However, these images have also captured unique wave patterns developed by the interaction of tsunami waves with land and with the bottom of the ocean in shallow water areas, moreover wave interaction between incoming and reflected waves from land boundaries were also observed. The observed wave pattern includes large scale wave reflection from land and refraction by sea bottom. In this work, we report basic wave properties derivated from these wave pattern images which were captured by SPOT–4 imagery.

Tsunami Effects on Shallow Waters : From Wave Scattering to Land Inundation

On 26 December 2004, one of the strongest Earthquake occurred in the Indian ocean of the Western coast of northern Sumatra, Indonesia. Measuring Mw = 9.3 mega–thrust, this Earthquake triggered a massive tsunami that struck the Indian ocean neighboring countries and Somalia. The devastating evidence of the damage caused by this highly destructive waves has been recorded via in–situ measurements and by satellite imagery. Based on our previous work with SPOT–5 imagery [6], where we reported observed tsunami wave properties such as interference, reflection and refraction generated by the trans– oceanic propagation of the tsunami off the coast of Thailand; coupled with recent reports on the extend, duration, speed and size of the Sumatra earthquake, we report a study of the effects that these traveling waves had on areas of shallow waters. Wave properties inferred from SPOT–5 images and numerical modeling, are used to calculate wave run–up and water penetration and inundation levels of the nearby beaches. Near shore we use shallow–water theory to calculate the evolution and runup of the emerging non breaking waves by first deriving several sea–surface profiles for the leading wave of a tsunami. As a complementary step, runup and inundation model calculations are compared with independent results obtained from detailed damage assessment performed on pre– and post– tsunami images of the affected region.

High Spectral Resolution Lidar and MPLNET Micro Pulse Lidar aerosol optical property retrieval intercomparison during the 2012 7-SEAS field campaign at Singapore

From August 2012 to February 2013 a High Resolution Spectral Lidar (HSRL; 532 nm) was deployed at that National University of Singapore near a NASA Micro Pulse Lidar NETwork (MPLNET; 527 nm) site. A primary objective of the MPLNET lidar project is the production and dissemination of reliable Level 1 measurements and Level 2 retrieval products. This paper characterizes and quantifies error in Level 2 aerosol optical property retrievals conducted through inversion techniques that derive backscattering and extinction coefficients from MPLNET elastic single-wavelength datasets. MPLNET Level 2 retrievals for aerosol optical depth and extinction/backscatter coefficient profiles are compared with corresponding HSRL datasets, for which the instrument collects direct measurements of each using a unique optical configuration that segregates aerosol and cloud backscattered signal from molecular signal. The intercomparison is performed, and error matrices reported, for lower (0-5km) and the upper (>5km) troposphere, respectively, to distinguish uncertainties observed within and above the MPLNET instrument optical overlap regime.

Characterization of aerosol physical and optical properties from a combination of ground-based and hand-held Sun-photometer data of Singapore

Since October 2006, the Center for Remote Imaging, Sensing and Processing (CRISP) of the National University of Singapore has joined the Aerosol Robotic Network, AERONET, to monitoring aerosol optical properties in this region. This initiative complements the already existing activities on satellite remote sensing performed at CRISP. In Singapore, the sources of aerosols are mostly from fossil fuel burning (energy stations, incinerators, cars etc.) and from the industrial and urban areas. The proximity to the sea adds a possible oceanic source and depending on the time of the year, there can be a strong bio-mass component coming from forest fires from various regions of the neighboring countries. In this work, we present a survey of aerosol optical depth (AOD) and Angstrom exponent retrievals at several regions of Singapore. AOD measurements were performed with the help of AERONETs CIMEL Sun-photometer (located at CRISP) and a versatile hand held Microtops II Sun-photometer. In order to identify the degree of geographical variability of aerosol optical properties, we collected data samples over selected sites across the island. Furthermore, we extracted concurrent data points from our own AERONET site in order to check for consistency and validation of our results. This study has enabled us to identify possible aerosol sources and understand the nature and physical characteristics of atmospheric aerosols across Singapore.

Atmospheric correction of IKONOS with cloud and shadow image features

In this paper, we present a method for atmospheric correction that uses the cloud and shadow image features. An iterative scheme is formulated to computes the ratio of diffuse to direct irradiance as well as the path radiance using the radiance detected over the open water and shadow pixels. These parameters are then used to compute the cloud and water reflectance. We implemented this method on IKONOS images which are known to have inferior signal to noise ratio compared to sensors specially designed for ocean color measurements. The corrected image reflectance over water pixels are compared to field measurements.

Sensitivity experiments of WRF-ARW PBL schemes over Singapore region: Impact of land use, land cover and model resolution

In the present study, the surface meteorological parameters over Singapore are simulated using WRF-ARW mesoscale model by varying the planetary boundary layer (PBL) parameterization schemes, horizontal resolutions and two land cover data sets (USGS and MODIS). Simulations are conducted with four nested domains having horizontal resolution of 27, 9, 3 and 1 km; 51 vertical levels by using the 1° × 1° NCEP final analysis meteorological fields for initial and boundary conditions. Eight days (20–28 January 2015) are selected for simulating various surface meteorological parameters. The model-simulated parameters of surface temperature, relative humidity, wind speed and wind direction are validated with the available observations over Singapore. It has been found that, improvements in predicting surface meteorological parameters with the increase in model resolution up to 3 km. The experiment with the 3 km grid resolution showed better simulated surface meteorological variables than that of 1 km resolution grid. Further, MODIS land cover data considerably improved the prediction of surface meteorological variables compare to the USGS. The surface meteorological variables simulated using the ACM2 PBL scheme with MODIS data are in better agreement with the observations showing least error statistics than the other PBL schemes used in the study. The better performance by ACM2 could be due to the non-local turbulence closure during unstable conditions and local-closure during stable conditions formulated in this scheme.