We have developed a multiwavelength Scanning Standoff Time-Resolved Raman spectroscopy (S2TR2S)
system to detect minerals and chemicals from a long distance (10-100 m) over a large area. The
multiwavelength SSTRRS system uses 532 and 785 nm pulsed lasers and two separate 5x beam expanders to
excite spontaneous Raman spectra of the chemicals with 10 mm diameter laser beams. The VIS-NIR system
employs a common Meade telescope (F/10, aperture 20.3 cm). In order to improve detection efficiency, the
light collected by the telescope is directly coupled into two f/1.8 transmission spectrograph covering the VIS
and NIR spectral regions by changing the volume Holographic Raman gratings for 532 and 785 nm laser lines,
respectively. The spectrograph is equipped with a gated intensified CCD camera and edge filters are used to
reject the reflected and Rayleigh scattered laser light. The S2TR2S system is operated using pan-tilt pointing
capability for precise measurements of selected distant points (under computer control). By making standoff
Raman measurements over a predefined grid array, a large area can be sampled and Raman composition maps
are constructed off the distant target area. This mapping capability of the instruments has been used to identify a
wide variety of minerals and hazardous chemicals from their Raman fingerprints and Raman images. The use of
pulsed laser and gated detection allow the measurement of the Raman spectra of minerals with minimum
interference from photoluminescence from transition metal ions and rare-earths ions, and ambient light.
The “Standoff Biofinder” is a powerful “search for life” instrument that is able to detect biomolecules from a collection of rocks and minerals in a large area with detection time less than a second using a non-contact, non-destructive approach. Biological materials show strong, short-lived fluorescence signals when excited with ultraviolet-visible (UVVis) wavelengths. The Standoff Biofinder takes advantage of the short lifetimes of bio-fluorescent materials to obtain real-time images showing the locations of biological materials among luminescent minerals in a geological context. The Standoff Biofinder uses an expanded and diffused nanosecond pulsed laser to illuminate a large geological region and a gated detector to record time-resolved fluorescence images. The instrument works in daylight as well as nighttime conditions and bio-detection capability is not affected by the background light. The instrument is able to detect both live and dead biological materials, and is a useful tool for detecting the presence of both extant and extinct life on a planetary surface. The Standoff Biofinder instrument will be suitable for locating fluorescent polyaromatic hydrocarbons, amino acids, proteins, bacteria, biominerals, photosynthetic pigments, and diagenetic products of microbial life on dry landscapes and Ocean Worlds of the outer Solar System (e.g., Enceladus, Europa, and Titan). An important feature of the Standoff Biofinder instrument is its capability to detect biomolecules which are inside ice, without sample collection.
The University of Hawaii has been developing portable remote Raman systems capable of detecting chemicals in
daylight from a safe standoff distance. We present data on standoff detection of chemicals used in the synthesis of
homemade explosives (HME) using a portable standoff Raman system utilizing an 8-inch telescope. Data show that
good-quality Raman spectra of various hazardous chemicals such as ammonium nitrate, potassium nitrate, potassium
perchlorate, sulfur, nitrobenzene, benzene, acetone, various organic and inorganic chemicals etc. could be easily obtained
from remote distances, tested up to 120 meters, with a single-pulse laser excitation and with detection time less than
1 μs. The system uses a frequency-doubled Nd:YAG pulsed laser source (532 nm, 100 mJ/pulse, 15 Hz, pulse width
10 ns) capable of firing a single or double pulse. The double-pulse configuration also allows the system to perform
standoff LIBS (Laser-Induced Breakdown Spectroscopy) at 50 m range. In the standoff Raman detection, the doublepulse
sequence simply doubles the signal to noise ratio. Significant improvement in the quality of Raman spectra is
observed when the standoff detection is made with 1s integration time. The system uses a 50-micron slit and has spectral
resolution of 8 cm-1. The HME chemicals could be easily detected through clear and brown glass bottles, PP and HDPE
plastic bottles, and also through fluorescent plastic water bottles. Standoff Raman detection of HME chemical from a 10
m distance through non-visible concealed bottles in plastic bubble wrap packaging is demonstrated with 1 s integration
time. Possible applications of the standoff Raman system for homeland security and environmental monitoring are
discussed.
We have used two-dimensional correlation on two-dimensional extinction cross-sections measured by a scanning lidar to determine the velocity structure of the salt-spray aerosols. The lidar scans were collected over a reef at Bellows Beach, on the Northeast side of Oahu, Hawaii. The resulting velocity streamlines suggest that lifting of sea-spray aerosols as high as 200 m occurs in the vicinity of opposing horizontal roll vortices. The velocities vary rapidly over distances of less than 500 m and show a complex pattern which is inadequately represented by conventional anemometer measurements.
When aerosol from the Hawaii volcano plume are present then the water leaving radiance derived from the SeaWifs satellite using the SeaDas algorithm is too large. It is shown that this problem may be due to the use of an incorrect aerosol model. Furthermore, it is shown that using longer wavelengths may be needed to solve the atmospheric correction problem under Hawaii volcanic aerosols.
The University of Hawaii routinely collects direct broadcast MODIS images over Hawaii. Using this data set we process real time satellite images of aerosol optical depths around Hawaii using our custom algorithm. MODIS channels 1 and 2 (~ 645 and ~ 858 nm) are used to derive aerosol optical depth spatial and temporal properties. The use of MODIS channels 1 and 2 provides images with 250 m resolution resulting in improved cloud detection. Due to this improvement, background aerosol optical depths values remain low even in regions of many small clouds. Although cloud rejection is not expected to be perfect, using 250 m resolution data provides a significant improvement over 1 km resolution data. In order to correct for surface reflection, meso-scale wind fields from the Regional Spectral Model (from the National Center for Environmental Prediction) and synoptic scale winds (from National Center for Environmental Prediction) are interpolated to the satellite pixel size. The use of meso-scale wind fields is required for the complex wind fields in and around the Hawaiian Islands. Here we will discuss the aerosols encountered in Hawaii, and provide examples of interesting aerosol optical depth images around Hawaii.
A small portable lidar system was recently used to derive aerosol optical concentrations from ground and aircraft platforms. The mini lidar uses a telescope setup with a relatively wide field of view allowing for measurements from close in (~60 m range) with no near field correction. In order to account for the large dynamic range, a custom logarithmic amplifier is used. Lidar measurements have been made in Hawaii and examples will be shown. More recently the Lidar was mounted on an aircraft for an experiment in the United Arab Emirates. In this case, the Lidar system was used to looking up, forward and down. The Lidar measurements looking up and down provided vertical profiles of aerosol concentrations. The lidar looking forward were used to derive quantitative aerosol extinction values using an existing and a new approach. Preliminary examples of this UAE data are shown. Being able to model aerosol phase functions is important for both satellite and Lidar aerosol retrievals. Mie theory is adequate for spherical particles but complex aerosols such as dust and organics are more difficult to model. Here we discuss phase function measurements we have made with our ground based polar nephelometer for sea salt and more recently for dust in the United Arab Emirates.
There is a need for portable, low-cost lidar systems that can be used for cloud, aerosols and chemical monitoring from a stand-off distance. At the University of Hawaii we have developed lidar systems based on a 12.7-cm diameter telescope and a 20 Hz frequency-doubled Nd:YAG laser source. For stand off Raman detection of organic liquid and vapors, and plastic explosives, we are using a 0.25-m HoloSpec f/2.2 spectrometer equipped with a gated intensified detector (PI Model I-MAX-1024-E). The samples of interest are excited with 532-nm laser light (35 mJ/pulse). The operational range of the Raman system is in 10's of meters and has been tested at distance of 66 m. This system can also be operated as a Raman lidar by using appropriate filters for atmospheric nitrogen, oxygen and other gaseous species of interest. The Mie-Rayleigh lidar system uses the same telescope and laser, but we have three (1064, 532 and 355-nm) wavelengths available for monitoring clouds and aerosols. A small Hamamatsu H6779 photomultiplier tube (PMT) located near the focal point of telescope detects 532-nm backscatter signal. An avalanche photodiode (APD, EG & G C3095) detector equipped with a 2.5-cm diameter aspheric lens is used for detecting 1064-nm backscatter. The Mie-Rayleigh lidar has usable range of 60 - 4000 m. Results obtained with this system for marine aerosols and clouds are discussed.
We present the results of our multi-wavelength scanning lidar investigations of time dependent 3-D marine aerosol fields as a function of meteorological parameters at a coastal site in Hawaii. We describe our measurements of salt-aerosol plumes generated at a reef >1.3 km from the lidar and their effect on the aerosol extinction coefficient. At typical trade wind speeds of ~7 m/s, plumes of salt spray have been observed to rise to heights of about 50 m above the reef. A time sequence of vertical scans at three wavelengths (355, 532, 1064 nm) was taken under light (1.9 m/s) wind conditions over the same reef. Large salt plumes more than 600 m high were found to develop under these conditions. The much greater height of light-wind plumes suggests that they are being dispersed less rapidly, allowing them to rise to greater heights because of the presence of thermals. Earlier data collected at Bellows showed reef plumes rising to 120 m in winds of 5 m/s, indicating a consistent trend of increasing plume height with decreasing wind speed.
Due to the complexity of atmospheric aerosol, validation efforts are required to test satellite retrievals. Here we give an overview of our aircraft and ship validation measurements near Hawaii. Some examples of the measurements are shown which illustrate some of the variability we have encountered. This effort is ongoing and can provide important background measurements for satellite validation as well as radiation studies.
Lidars are ideal for mapping the spatial distribution ofaerosol concentrations, however efforts to convertthe lidar measurements into estimates of the aerosol extinction or scattering coefficient are usually complicated. The difficulties arise from the uncertainty in the aerosol backscatter-to-extinction ratio and the lidar calibration. In marine conditions with little absorption, the aerosol backscatter-to-extinction ratio is identical to the aerosol phase function/4? at 1 80 degrees (backscatter) . Uncertainty in the lidar calibration is another source ofuncertainty, which can change with time depending on the state ofthe optics (clean or dirty). Here we investigate several techniques to obtain calibrated aerosol extinction coefficient values. The first approach uses horizontal lidar measurements over the open ocean where the atmosphere is horizontally homogeneous. The lidar calibration or aerosol phase function is adjusted until the derived aerosol extinction coefficients are flat with distance. Modeling shows that this provides correct aerosol extinction values. A second approach uses a target to reflect the lidar beam at different distances. The aerosol extinction is derived from the differential transmission measurements. As an independent measurement, the aerosol phase function and scattering coefficients can be measured with a polar nephelometer.
On the windward side of Oahu, a multi-wavelength Mie-Rayleigh (MR) scanning lidar is used on a regular basis for measuring aerosol attenuation in the marine boundaiy layer. The lidar data are being used for investigathg dynamic effects of marine aerosol fields on electro-optical (EO) properties. The lidar has been operated mostly at 532 and 1064 nm, and recently at 355 nm. We have observed that the vertical aerosol distribution can be very non-uniform. Under certain atmospheric conditions, ascending and descending streaks of aerosols with high extinction (2x 1O-4 per meter) have been observed, indicating that both the surface and cloud drizzle effects are important. Horizontal lidar scans at 6 meters above the sea surface indicate that aerosol is fairly uniform on a large scale but can exhibit significant variability on small scales particularly close to protruding reefs and shorelines. Above the reefthe enhanced aerosol fields have been observed to rise as high as 100 meters. As expected there is a strong correlation between wind speed and sea salt extinction values. The temporal and spatial distribution ofthese aerosol fields and their dependence meteorological parameters and wave height are discussed.
A ship radiometer is currently being constructed which will make sun, sky and ocean surface multi-wavelength radiance measurements. The measurements will be used to derive aerosol and ocean surface optical properties. This paper describes the basic design of this radiometer.
The ability to derive aerosol properties from satellites is important for climate change studies and atmospheric corrections in studying surface properties. Although aerosols have been measured over land from satellite, it is more feasible to measure them over low surface albedos such as the ocean. One of the uncertainties that must be dealt with is the aerosol phase function, which depends on the aerosol size distribution and the observing wavelength.
In recent years aerosol optical depths have been estimated from AVHRR satellite images on a regular basis. One of the primary uncertainties of these methods is in the choice of the aerosol phase function. In this paper the possibility of using the ratio of AVHRR channel 1 and channel 2 to infer the value of the aerosol phase function is studied. For this purpose a large number of marine aerosol measurements are employed to study the response of NOAA AVHRR satellites for various aerosol cases.
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