It is understood that atmospheric turbulence results in fluctuations in the received power of an electro-optical (EO) link, a phenomenon known as optical scintillation. The atmospheric variable relevant to optical scintillation is the structure function parameter (Cn2) which can be quantified through optical scintillation measurements or derived from measurements of high-rate sampled atmospheric turbulence, especially the temperature perturbations. In addition to this (Cn2) can be estimated using models, some of which are based on surface layer similarity theory. However, the near shore marine atmospheric surface layer (MASL) provides an optically heterogeneous and complex turbulent environment that can be difficult to model accurately. A better understanding of the characteristics of near shore surface layer scintillation will provide increased exploitation of the environment by current and future EO systems operating in littoral regions. In an effort to better determine the scintillation effects in the MASL, observations were taken during the 26-day Couple Air-Sea Processes and Electromagnetic ducting Research West coast (CASPER-West) field campaign in September - October 2017 off the coast of Pt Mugu, CA.
In this paper, we introduce the CASPER-West EO component to include a description of the operating area, major platforms and major instruments relevant to EO measurements, and sampling strategy. We show comparisons of the derived (Cn2) from scalar perturbation measurements, bulk model parameterization, and from concurrent scintillation measurements between the R/V Sally Ride and R/P FLIP. Slant path optical links between a remotely piloted hexa-copter and the R/P FLIP were also available. Both stable and unstable thermal stratifications of the MASL were encountered throughout the campaign and we will discuss the observed differences between the experiment and those from current similarity theories in these different stability conditions.
Electro-optical (EO) and infrared (IR) signals propagating through the atmosphere exhibit intensity fluctuations caused by atmospheric turbulence, a phenomenon known as scintillation. Scintillation is directly related to the refractive index structure parameter Cn2 defined as the refractive index structure function scaled to for the turbulence inertial subrange. Quantifying Cn2 is essential to evaluate and predict scintillation effects on EO/IR systems. Meanwhile, aerosols in the lower atmosphere absorb and scatter EO/IR energy, resulting in attenuation, aliasing, and blurring.
We will present initial results on Cn2 and aerosol variability in the coastal zone using simultaneous measurements from a Twin Otter research aircraft, two instrumented ocean vessels [R/V John Martin and a rigid hull inflatable boat (RHIB)] , and a coastal land site. All measurements were taken as part of the Coastal Electro-Optical PropagaTion eXperiment (CEOPTeX) conducted in April/May 2016 offshore of Moss Landing, CA. Aerosol concentration, scattering, and absorption were obtained from the research aircraft in the atmospheric boundary layer. Cn2 was derived from measurements of temperature and humidity sampled at 20 Hz from all platforms/site. Two level Cn2 measurements were also taken when the R/V John Martin and the RHIB were co-located. We will discuss the spatial/temporal variability of the measured quantities, and the difference between the Cn2 at the coastal region and those predicted by surface layer similarity theory and the measured bulk quantities.
Analysis of bulk-skin sea surface temperature (SST) difference form the west and east coasts of United States is presented using the data collected from three field experiments. These experiments were conducted at offshore Duck, North Carolina and in the Monterey Bay of the California coastal region. Bulk SST measurements were made using conventional thermistors from a depth of one meter below the sea level. Infrared radiometers were used to measure the surface skin SST. Depending on measurement depth and prevailing conditions, the bulk SST can differ from skin SST by few tenths of a degree to O(1°C). Difference between bulk and skin SST arise from cools skin and warm layer effects. Bulk-skin SST difference (ΔSST) estimated from east coast observations varied from -0.46°C to 1.24°C. Here, the bulk SST was higher than skin SST most of the time during the observations. This indicates cool skin effect was the dominant factor determining the ΔSST in the east coast. For wind speeds less than 4 m s-1, we also noticed an increase in ΔSST. Additionally, for low winds (<4 m s-1) ΔSST also varied diurnally with the occurrence of generally higher ΔSST in the nighttime in comparison with daytime. Moreover, increase in downwelling longwave radiation reduced the bulk-skin SST difference. ΔSST calculated from the observation in the Monterey bay varied between ~2.3° and ~-2.3°C. This was higher than the variability ΔSST observed at the east coast. Moreover, ΔSST variability observed at west coast was independent of wind speed.
KEYWORDS: Radar, Reflectivity, Liquids, Signal to noise ratio, Temporal resolution, Doppler effect, Spatial resolution, Signal attenuation, Particles, Classification systems
The Micro Rain Radar (MRR) a highly resolution radar operates at a frequency of 24 GHz installed at Thumba
(8.5°N, 76.9°E) under Ka band propagation experiment is used extensively to characterize the tropical rain. This radar
measurements of rain were obtained with fine spatial and temporal resolutions like One minute time resolution and 200
m height resolution. With this radar for the first time classification of precipitating systems are studied. With the
presence or absence of bright band a radar signature of melting layer one can classify particular rain type as convective
or stratiform. For present study MRR data from September 2005 onwards are collected. The main objective is to classify
precipitation system into Stratiform and Convective with the presence or absence of Bright band. Another potential of
this radar is ability to give information of vertical structure of fall velocity of hydrometeors. This also gives profiles of
number concentration of various ranges of Drop sizes, liquid water content and rain rate for different heights. These
results are compared with the collocated ground based Disdrometer. Attenuation at Microwave frequencies during the
presence of rain is a serious concern to the communication. Once temporal and spatial information of DSD is known
microwave attenuation can be studied. These results will be presented in this paper.
Tropical regions can be characterized as large fields of convective clouds of all sizes. Latent heat released is
different for different precipitating systems like convective and stratiform. So we need to classify various precipitating
systems. In the present study, ground based observations of Joss-Waldvogel Disdrometer (JWD) which was installed at
Thumba (8.5°N, 76.9°E) under Ka band propagation experiment is used extensively to characterize the tropical rain. It
can be noticed that the JWD is placed at calm and noise-free places, in order to make it sensitive to smaller drops. The
JWD is a standard tool for precipitation measurements such as Drop Size Distribution (DSD), rainfall intensity, R, rain
accumulation and liquid water content, W, reflectivity factor, Z. The range of drop diameters that can be measured spans
from 0.3 to 5 mm with an accuracy of 5%. For present study Disdrometer data from June 2005 onwards are collected.
The main objective of the present study is to classify precipitation system into Convective, Transition (an intermediate
region) and stratiform. Since DSD integral parameters like rain rate (R), liquid water content (LWC), Reflectivity (Z) are
different for different precipitating systems, so we need to classify these systems. There is a dearth of raindrop Size data
and distribution models for the tropics, especially over Indian continent. Models for drop size distribution are required
for the evaluation of microwave and millimeter wave propagation effects due to rainfall. In the present paper various
DSD models namely gamma model and lognormal model with different combination of moments for observing the
characteristic features of tropical rain are studied.
A case study of sea breeze circulation at a coastal region Thumba (8.5°N, 76.9°E) was carried out using Doppler Sodar,
surface wind, temperature, humidity measurements and radiosonde ascents. The analysis of surface meteorological data
showed that the onset of sea breeze on 12th April 2006 was at 0945 hrs. GPS sonde observation over sea at 1425 hrs and
Radiosonde observation over land at 1730 showed a well developed sea breeze circulation over Thumba coast by
afternoon hours. The vertical extent of sea breeze circulation was ~1000m over sea as well as on land. The Thermal
Internal Boundary Layer (TIBL) depth associated with sea breeze circulation was about 400m at 8 km away from coast.
The marine mixed layer height was ~500m about 12 km away from the coast. Numerical simulation of sea breeze was
made using HRM (High Resolution Model) and compared the results with the observations.
Enhanced aerosol loading over the Indo-Gangetic Plain (IGP) is a regular feature during winter months. In addition to the environmental degradation and reduced visibility, these aerosols can cause significant radiative impact also. In view of this, a campaign mode observation under ISRO-GBP was conducted in December 2004 to characterize the aerosol properties over the IGP. As part of this, extensive measurements of aerosol BC were made from Kharagpur, an inland rural location lying at the eastern end of the Indo Gangetic Plain. It also lies close to several industrialized regions and area having lot of mining activities
Results showed, extremely high BC concentration, often exceeding ~20 mg m-2, prevailed during December. During this period, BC concentration also showed large diurnal variation. Simultaneous measurements of the local atmospheric boundary layer height and wind fields revealed a very close association between the BC concentration and the ventilation coefficient (defined as the product of the boundary layer height and the transport wind). Back trajectory analyses using HYSPLIT revealed that in addition to the local boundary layer dynamics, the changes in the advection pathways also influence the concentration of BC.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.