Impact of Multiple Satellite Ocean Color Samplings in a Day on Assessing Phytoplankton Dynamics

ZhongPing Lee,Mingshun Jiang,Curtiss Davis,Nima Pahlevan,안유환,Ronghua Ma 한국해양과학기술원 2012 Ocean science journal Vol.47 No.3

Ocean-color imagers on conventional polar-orbiting satellites have a revisit time of ~2 days for most regions, which is further reduced if the area is frequently cloudy. The Geostationary Ocean Color Imager (GOCI), the first ocean-color imager on a geostationary satellite, provides measurements 8times a day, thus significantly improving the frequency of measurements for studies of ocean environments. Here, we use results derived from GOCI measurements over Taihu Lake to demonstrate that the extra sampling can be used to improve the accuracy of statistically averaged longer-term (daily) measurements. Additionally, using numerical simulations, we demonstrate that the coupling of diurnal variations of both biomass and photosynthetic available radiation can improve the accuracy of daily primary production estimates. These results echo that higher sampling frequency can improve our estimates of longer-term dynamics of biogeochemical processes and highlights the value of ocean color measurements from geostationary satellites.

Removal of surface-reflected light for the measurement of remote-sensing reflectance from an above-surface platform

Lee, ZhongPing,Ahn, Yu-Hwan,Mobley, Curtis,Arnone, Robert The Optical Society 2010 Optics express Vol.18 No.25

<P>Using hyperspectral measurements made in the field, we show that the effective sea-surface reflectance ? (defined as the ratio of the surface-reflected radiance at the specular direction corresponding to the downwelling sky radiance from one direction) varies not only for different measurement scans, but also can differ by a factor of 8 between 400 nm and 800 nm for the same scan. This means that the derived water-leaving radiance (or remote-sensing reflectance) can be highly inaccurate if a spectrally constant ? value is applied (although errors can be reduced by carefully filtering measured raw data). To remove surface-reflected light in field measurements of remote sensing reflectance, a spectral optimization approach was applied, with results compared with those from remote-sensing models and from direct measurements. The agreement from different determinations suggests that reasonable results for remote sensing reflectance of clear blue water to turbid brown water are obtainable from above-surface measurements, even under conditions of high waves.</P>

Uniform spacing interrogation of a Fourier domain mode-locked fiber Bragg grating sensor system using a polarization-maintaining fiber Sagnac interferometer

Lee, Hwi Don,Jung, Eun Joo,Jeong, Myung Yung,Chen, Zhongping,Kim, Chang-Seok IOP Pub 2013 Measurement Science and Technology Vol.24 No.6

<P>A novel linearized interrogation method is presented for a Fourier domain mode-locked (FDML) fiber Bragg grating (FBG) sensor system. In a high speed regime over several tens of kHz modulations, a sinusoidal wave is available to scan the center wavelength of an FDML wavelength-swept laser, instead of a conventional triangular wave. However, sinusoidal wave modulation suffers from an exaggerated non-uniform wavelength-spacing response in demodulating the time-encoded parameter to the absolute wavelength. In this work, the calibration signal from a polarization-maintaining fiber Sagnac interferometer shares the FDML wavelength-swept laser for FBG sensors to convert the time-encoded FBG signal to the wavelength-encoded uniform-spacing signal.</P>

Microstructure Selection in the Interdendritic Region During Directional Solidification of a Ni-23at.%Al Alloy

Zhongping Que,Jiho Gu,Jongho Shin,정연길,Jehyun Lee 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.1

Directional solidification experiments of a binary Ni-23at.%Al alloy were carried out to examine the effectsof growth velocity on the microstructure selection in the interdendritic region. Only the growth velocity waschanged from 5 µm/s to 60 µm/s under a given thermal gradient. As a result, the noticeable change in themicrostructure during solidification occurred between the γ dendrites. The γ interdendritic microstructure wasvaried as a function of growth velocity from rod γ-γ' coupled peritectic structure to planar γ' structure andthen to eutectic structures consisting of stable γ'-β eutectic and metastable γ-β‚ eutectic structures. Themicrostructure selected preferentially among the γ dendrites was considered by calculating the interfacetemperature of a phase growing into its parent melt. It is shown that the microstructure selection in the γinterdendritic region is determined by a phase or a structure kinetically leading at the highest interfacetemperature under a given growth condition.

Optimization for Axial Resolution, Depth Range, and Sensitivity of Spectral Domain Optical Coherence Tomography at 1.3 μm

Sang-Won Lee,Hyun-Woo Jeong,Beop-Min Kim,Yeh-Chan Ahn,Woonggyu Jung,Zhongping Chen 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6

We have developed high-speed and high-resolution spectral domain optical coherence tomography at 1.3 μm using an InGaAs line-scan camera and a broadband light source with the bandwidth of 170 nm that produces a theoretical axial resolution of 4.4 μm in air. We compared axial resolutions from point spread functions (PSFs) and depth ranges while changing the full spectral bandwidth detected by the camera and describing the optimization process for the axial resolution, the depth range, and the sensitivity for SD-OCT system. We found that SD-OCT at 1.3 μm cannot satisfy the conditions both below the axial resolution of 5 μm and above the depth range of 2 mm because of the restricted pixel number of the line-scan camera. To scan a large depth range, the axial resolution has to be sacrificed. In addition, the sensitivity rolls off slowly as a function of the depth if a large depth range is scanned. On the other hand, if the axial resolution needs to be close to the theoretical one, the depth range becomes limited and the sensitivity decays quickly. Since we have to maintain a reasonable depth range of 2.0 mm, we chose the spectrum full bandwidth of 214 nm captured by the detector to balance the axial resolution of 8.2 μm. In this setting, the sensitivity of our OCT system was measured at 107.1 dB. Theoretical and experimental results are compared and presented in this paper. We have developed high-speed and high-resolution spectral domain optical coherence tomography at 1.3 μm using an InGaAs line-scan camera and a broadband light source with the bandwidth of 170 nm that produces a theoretical axial resolution of 4.4 μm in air. We compared axial resolutions from point spread functions (PSFs) and depth ranges while changing the full spectral bandwidth detected by the camera and describing the optimization process for the axial resolution, the depth range, and the sensitivity for SD-OCT system. We found that SD-OCT at 1.3 μm cannot satisfy the conditions both below the axial resolution of 5 μm and above the depth range of 2 mm because of the restricted pixel number of the line-scan camera. To scan a large depth range, the axial resolution has to be sacrificed. In addition, the sensitivity rolls off slowly as a function of the depth if a large depth range is scanned. On the other hand, if the axial resolution needs to be close to the theoretical one, the depth range becomes limited and the sensitivity decays quickly. Since we have to maintain a reasonable depth range of 2.0 mm, we chose the spectrum full bandwidth of 214 nm captured by the detector to balance the axial resolution of 8.2 μm. In this setting, the sensitivity of our OCT system was measured at 107.1 dB. Theoretical and experimental results are compared and presented in this paper.

Effect of Metabolic Structures and Energy Requirements on Curdlan Production by Alcaligenes faecalis

Zheng, Zhi-Yong,Lee, Jin-Woo,Zhan, Xiao Bei,Shi, Zhongping,Wang, Lei,Zhu, Li,Wu, Jian-Rong,Lin, Chi Chung Korean Society for Biotechnology and Bioengineerin 2007 Biotechnology and Bioprocess Engineering Vol.12 No.4

A comprehensive metabolic network was proposed for Alcaligenes faecalis and employed in a stoichiometrically based flux balance model for curdlan production optimization. The maximal yield of curdlan was evaluated for curdlan batch production. Various metabolic structures and metabolic pathway distributions related with the curdlan maximal yield was evaluated. The results showed that the energy efficiency rather than the substrate supply was the major constraint for the enhancement of curdlan production. The increase in specific rate of glucose uptake could enhance curdlan production yield due to the decrease of the ratio of metabolic maintenance to substrate consumption. However, some of the energy loss and nutrient limitation associated with the increase of metabolic maintenance would adversely affect the conversion efficiency of the substrate.

Evaluation of GOCI Sensitivity for At-Sensor Radiance and GDPS-Retrieved Chlorophyll-a Products

Chuanmin Hu,Lian Feng,ZhongPing Lee 한국해양과학기술원 2012 Ocean science journal Vol.47 No.3

The signal-to-noise ratio (SNR, or sensitivity) of an ocean color instrument is a critical parameter to determine the accuracy and precision of the data products. Yet published literature showed various formats in SNR specifications under different conditions, making a direct cross-sensor comparison difficult. Here, we compared the SNRs of GOCI spectral bands with those of SeaWiFS and MODIS/Aqua under the same radiance inputs. We also compared their ability to resolve small changes in the retrieved chlorophyll-a data products (Chl). While GOCI visible bands showed similar at-sensor SNRs to SeaWiFS, the near-infrared (NIR) bands showed significantly higher SNRs. Because the NIR bands were used for atmospheric correction, the increases in SNRs led to reduced noise in the retrieved Chl, as shown in the GOCI and SeaWiFS Chl products for Chl < 0.1 mg m-3. The noise in the retrieved products also depends on the retrieval algorithms in addition to the sensor SNR. When a new band-subtraction algorithm (the Ocean Color Index or OCI algorithm) was applied to the same GOCI remotesensing reflectance data derived from the GDPS software package, significant noise reduction was found in the Chl product for low concentrations (< 0.25 mg m-3), leading to product precision (~3% in Chl) comparable to those from MODIS/Aqua measurements. This is certainly a significant achievement, as GOCI spatial resolution is much higher than MODIS (500 m versus 1 km). In addition, artifacts across image mosaic edges over low-concentration waters have been removed nearly completely by the OCI algorithm. Data analyses also indicated that GOCI radiometric calibration requires further improvement.

Effect of Metabolic Structures and EnergyRequirements on Curdlan Production byAlcaligenes faecalis

Xiao Bei Zhan,Zhi-Yong Zheng,Jin Woo Lee,Zhongping Shi,Lei Wang,Li Zhu,Jian-Rong Wu,Chi Chung Lin 한국생물공학회 2007 Biotechnology and Bioprocess Engineering Vol.12 No.4

A comprehensive metabolic network was proposed for Alcaligenes faecalis and employed in a stoichiometrically based flux balance model for curdlan production optimization. The maximal yield of curdlan was evaluated for curdlan batch production. Various metabolic structures and metabolic pathway distributions related with the curdlan maximal yield was evaluated. The results showed that the energy efficiency rather than the substrate supply was the major constraint for the enhancement of curdlan production. The increase in specific rate of glucose uptake could enhance curdlan production yield due to the decrease of the ratio of metabolic maintenance to substrate consumption. However, some of the energy loss and nutrient limitation associated with the increase of metabolic maintenance would adversely affect the conversion efficiency of the substrate.

Ultrawideband photonic crystal fiber coupler for multiband optical imaging system

Young Ryu, Seon,Young Choi, Hae,Seo Choi, Eun,Tomov, Ivan,Chen, Zhongping,Ha Lee, Byeong The Optical Society 2010 Applied Optics Vol.49 No.10

<P>We report a photonic crystal fiber (PCF) coupler having an ultrawide spectral bandwidth keeping single mode operation. The use of the PCF coupler in a fiber-based optical coherence tomography (OCT) system enables us to handle the wide spectral bands of various light sources, including superluminescent diodes (SLDs) at 1300 nm and 820 nm, Ti:sapphire lasers, and white-light sources. The multiband imaging performances of the PCF-based OCT system are demonstrated by obtaining dental images at 1300 nm and 820 nm with the same setup. In addition, we show that the PCF coupler could cover the spectrum over a one octave span and guide both the fundamental wave (1030 nm) and the second harmonic wave (515 nm) simultaneously.</P>