Refraction measurements and modeling over the Chesapeake Bay during the NATO (TG-51) SAPPHIRE trials, June 2006

Jong, Arie N. de; Fritz, Paul J.

doi:10.1117/12.730396

Cited by 3 publications

(1 citation statement)

References 6 publications

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“…The participants from TNO-Defense, Security and Safety, NL, positioned a buoy about 6 km from CBD. At this device, air temperatures at different heights, water temperature, humidity and wind speed were measured (see also these proceedings, [8]). The water depth at the buoy location is more than 10 m and should suffice to conclude the water temperature along the measurement path.…”

Section: Meteorologymentioning

confidence: 99%

The SAPPHIRE trial: investigations on angular deviation caused by refraction

Stein

Seiffer

2007

SPIE Proceedings

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The NATO Panel SET-088 TG-51 has the charter to investigate infrared research topics relating to Littoral Ship Self-Defence. The two main research areas for TG-51 are low-altitude maritime IR propagation phenomenology and ship signature properties. Atmospheric scintillation and refraction prediction models were validated in several trials conducted by different NATO groups. So far most trials were conducted in cold waters. In June 2006, TG 51 performed the SAPPHIRE trial (Ship and Atmospheric Propagation PHenomenon InfraRed Experiment) to collect data in littoral areas under conditions of warm sea temperatures. The location of the trial was the US Naval Research Laboratory's Chesapeake Bay Detachment (CBD) field site on Chesapeake Bay. The objectives of the trial were to validate ship signature models and scintillation/refraction models. In the SAPPHIRE trial, the purpose of FGAN-FOM was to investigate the influence of changing weather conditions on the apparent elevation of a target. Therefore, we set up an IR-camera at CBD overlooking Chesapeake Bay observing a set of lights installed on an Island in 16 km distance. In this paper we discuss and analyse the measured elevations and compare them to the propagation model IRBLEM (IR Boundary Layer Effects Model) by DRDC, Canada.

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Section: Meteorologymentioning

confidence: 99%

The SAPPHIRE trial: investigations on angular deviation caused by refraction

Stein

Seiffer

2007

SPIE Proceedings

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Measurement of optical refraction, transmission, and turbulence effects in False Bay, South Africa: June 2007

2008

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Complementary to a measurement campaign of small surface targets in the False Bay, South Africa [1], a set-up could be arranged of atmospheric propagation experiments. This opportunity allowed us to collect another set of transmission data in a coastal area, where the environmental conditions are generally non-homogeneous and rapidly changing. It was found before, that the validity of models, predicting the aerosol size distribution, the vertical temperature profile or the structure constant for the refractive index C n 2 tends to be questionable in this type of areas [2,3]. Proper knowledge of the relation between the range performance of electro-optical and infrared sensors and in-situ weather parameters is however of key importance for operational use of this type of sensors, so the collection of additional propagation data was very relevant. Refraction data were collected continuously by using a geodetic theodolite with camera system over a 15.7 km path in the False Bay. Transmission-and scintillation data were collected over a 9.6 km path by means of our MSRT (MultiSpectral Radiometer Transmissometer) and a Celestron telescope (with camera) with a focal length of 1.25 m. Weather parameters were measured at a shore station and on a rock in the bay. The weather was greatly variable with many showers, while the visibility, cloudiness and ASTD (Air-Sea Temperature Difference) conditions were continuously changing. Analysis of the theodolite data delivered absolute AOA (Angle of Arrival) data, which have been compared with predictions from the bulk model for marine boundary layers and from two empirical two-parameter temperature profiles. Transmission data, collected in three spectral bands (around 0.6, 0.9 and 1.5 µm), provided information on the particle size distribution, assumed to be of a Junge type. Knowledge of this information allows the prediction of the atmospheric transmission in other spectral bands, including the IR. The transmission data were compared with the data from a visibility meter on the roof of the IMT building. Both data sets correlated reasonably well. From the high speed MSRT transmission data (integration time 10 ms, sampling rate 30 Hz) the scintillation index (SI) was calculated, which showed a reduction in SI value when it starts to rain, while the SI came back to normal shortly after the shower. The measured SI data were transformed into C n 2 values (the atmospheric refractive index structure function) and compared with predictions from the bulk model with different type of stability functions for a selected set of measurement periods. The model predictions show deficiences for conditions with small ASTD. The SI data from the MSRT were compared with the scintillation data, collected with the Celestron imaging system, which showed interesting correspondences and differences, which are discussed in the paper. From the Celestron data also the beam wander was determined, providing, similar to the SI, a source of information on C n 2 . It was shown, that the beam wander (blur) ...

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Measurement and prediction of optical turbulence effects as function of altitude in the marine boundary layer

2009

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The impact of atmospheric turbulence in the marine boundary layer on the performance of ship-borne and coastal optical and infrared surveillance sensors is well known. On the one hand, the detection process may benefit from scintillation of signals from point-like targets at long range, while target identification is hampered by turbulence induced blurring and beam wander. According to the commonly used turbulence model, based on the Monin-Obukhov similarity theory for the marine boundary layer (the so-called bulk model), the structure function for refractive index C n 2 decreases with altitude. This height dependence of C n 2 and the associated blurring, scintillation and beam wander, has consequences for the range performance of sensors against incoming small targets. In the paper, predictions of the height-dependence of turbulence, based upon the bulk model, will be given for a number of scenarios from previous measurement campaigns, such as POLLEX and SAPPHIRE. In these experiments, taking place in a variety of weather conditions (e.g. Air-Sea Temperature Difference (ASTD)), images were collected from vertical arrays of sources at long range. In addition imagery was collected of helicopters, acting as point-targets at ranges up-to more than 30 km. The imagery is used to determine turbulence effects, which are compared with the model predictions. The results of this comparison, showing details on the validity of the model, are presented in the paper.

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Refraction measurements and modeling over the Chesapeake Bay during the NATO (TG-51) SAPPHIRE trials, June 2006

Cited by 3 publications

References 6 publications

The SAPPHIRE trial: investigations on angular deviation caused by refraction

The SAPPHIRE trial: investigations on angular deviation caused by refraction

Measurement of optical refraction, transmission, and turbulence effects in False Bay, South Africa: June 2007

Measurement and prediction of optical turbulence effects as function of altitude in the marine boundary layer

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