Showing papers in "Cospar Colloquia Series in 1997"

Sensible Heat Flux Estimated by Using Satellite Data Over the North Pacific

Abstract: Turbulent heat fluxes over a wide region are generally estimated by an aerodynamic bulk formula. Though a remote sensing technique can be expected to estimate global heat flux, it is difficult to obtain every physical parameter included in aerodynamic formulae by a remote sensor. In particular it is difficult to obtain air temperature at sea surface by a remote sensor, which is needed to estimate sensible heat flux. In the present study new methods directly estimating sensible heat flux from latent heat flux and the Bowen ratio is proposed and examined. The results are validated with those estimated by ocean observation data and compared with satellite-derived flux by other methods.

Analyses of 1994 Typhoons in the Taiwan Region using Satellite Data

Abstract: Taiwan is situated in the prevalent typhoon track in the northwestern Pacific. On average, about one third of the island total annual precipitation is due to typhoons, with the other two third being contributed by the summer monsoon, or Meiyu, and wintertime large scale frontal rainfall. While the typhoons bring the needed moisture for agricultural consumption and industrial utilization, heavy rainfall associated with typhoons often result in large scale flooding and land slide. The prediction of the typhoon track and its severity is therefore a high priority topic both for operation and research. The severity of a typhoon can be defined in terms of the wind strength and the moisture content. The Special Sensor Microwave/Imager (SSM/I) on board of the Defense Meteorological Satellite Program (DMSP) satellites measures microwave radiation in 19.4, 22.2, 37, and 85.5 GHz. These measurements provide an opportunity to estimate parameters such as surface wind speed, water vapor and cloud water contents, and rainfall rate over oceans. In 1994, Taiwan experienced an above normal frequency of typhoon hits, five typhoons hit the island in two months. In this report, estimates of the moisture content of these typhoons are made based on the SSM/I measurements. An assessment of the relative strength of the typhoons are made with analyzed data.

A University Ground Station Facility for Microsatellite Tracking and Data Receiving

Abstract: This paper addresses the establishment and relevant accomplishments of a simple facility used for microsatellite tracking and data receiving in National Cheng Kung University. In conjunction with the Amateur Satellite (AMSAT) organization and its assistance, a ground station is successfully developed to execute the satellite tracking, telemetry transmission with several microsatellites on orbit, and multi-type telemetry data processing through the linkage of radio transceivers and a terminal node controller (TNC) monitored by a personal computer (PC) with tracking software. Through the establishment of the simple facility as presented here, it is strongly felt that not only the personnel involved are trained quickly, but also the required space technologies are gained with the minimum amount of budget investment. It is felt as well that this is a good way for developing and quickly getting involved in such kind of space activities in universities like NCKU where the student training in space technology plays the major role in professional education.

Regional Challenges for Development of Satellite Ocean Color Algorithms

Abstract: The planned launch of several ocean color sensors in the next few years will usher in a new era in oceanography in which a continuous time-series of global ocean color data will be available for 15-20 years With appropriate effort on the part of oceanographers and Earth scientists in applying ocean color data, it is not unreasonable to expect that this could become a perpetual time-series applied to monitoring the status of the Earth's carbon cycle To fulfill this objective, it is imperative to develop appropriate algorithms to retrieve not only surface phytoplankton pigments, but also primary production and the organic carbon exported from the surface photic zone to the ocean interior Challenges to these objectives, and some consideration of methods are presented

Search of Ocean Convergence Zones via the Observation of Whitecap Coverage Application to Fishery

Abstract: As known since long, some kinds of fish (e.g. pelagic) gather in frontal and/or convergence zones (Uda, 1952). On the other hand these current features result in enhanced wave breaking (Uda, 1938). It is of clear interest to utilize these properties for the fishery industry, and more, to apply remote sensing from space in that. The following topics of this scope are discussed in present paper. 1. Obviously mesoscale currents of 10-100 km size (rather then smaller ones) are the first candidate to be observable from space. Here some evidence of wavebreaking response to mesoscale currents are presented on the basis of our experiments. 2. An attempt to search the mesoscale zones of the greatest current gradients (or possible fishery regions) in Norwegian Sea is described. 3. Application of microwave radiometric technique to searching the oceanic current peculiarities from space is discussed on the basis of theoretical estimation.

Comparing NOAA-12 and Radiosonde Atmospheric Sounding Profiles for Mesoscale Weather Model Initialization

Abstract: Mesoscale meteorological models such as the MM5 model from NCAR utilize atmospheric sounding data from radiosondes to initialize numerical computations. Radiosondes are released twice daily from manned land-based weather stations, commonly located near population centers. Over remote land and oceanic regions, modellers commonly resort to previous 6 hour model predictions for initial conditions. As an alternative, satellite derived atmospheric soundings provide continuous spatial coverage at regular intervals irrespective of geographical location. With the recent installation of a remote sensing station at the Hong Kong University of Science & Technology for L-band polar orbiting satellites, comparison studies between radiosonde and satellite derived atmospheric soundings have been initiated. Microwave and infrared emission measurements from the NOAA-12 polar orbiting satellite were processed with a TOVS (Tiros Operational Vertical Sounder) retrieval software package developed by the University of Wisconsin to derive temperature, dew point, wind direction and speed. Comparisons were conducted when both soundings were within 60 km ground distance and 1 hour of release from each other. Vertical profiles were constructed for 9 standard atmospheric levels from radiosonde and TOVS soundings over the South China Sea region, between January 16 - May 11, 1995. Wind speed profiles were consistently biased from the associated radiosonde profiles. Interestingly, the profiles maintained a similar shape throughout the vertical domain. A preliminary examination of the MM5 model sensitivity to the identified offset will also be presented.

The Relationship Between Surface Chlorophyll a and Biogenic Matter in the Euphotic Zone in the Southern East China Sea in Spring

Abstract: Determining the standing stock of phytoplankton, inventory of particulate organic carbon and the primary production with remotely sensed ocean color, requires a thorough understanding of the relationship between the chlorophyll a concentration in the surface seawater within one optical depth and other biogenic matter in the euphotic zone. In this study, we investigated the downwelling irradiance of the photosynthetically available radiation (PAR) and chlorophyll a concentration in the sea off northern Taiwan. The log-log plot of the mean attenuation coefficient vs. the average chlorophyll a concentration within the euphotic zone in the sea off northern Taiwan exhibited a linear trend. Consequently, the euphotic zone depth is log-linearly dependent on the average pigment concentration (chlorophyll a + phaeopigment) within the euphotic zone, similar to that observed for the "Case I" water by Morel (1988). Because the Kuroshio water strongly influences upon the shelf waters off northern Taiwan under the prevailing northeast monsoon in spring, it is reasonable to assume that the shelf waters in the southern East China Sea belong to the "Case I" water in terms of bio-optical properties. Under this assumption, the euphotic zone depths in this region were calculated and the inventories of biogenic matter were integrated over the euphotic zone. The inventories of chlorophyll a and pigment concentrations corresponded well with the average concentrations of chlorophyll a and pigment within one optical depth, respectively. A reasonably good correlation was found between the concentration of the particulate organic carbon (POC) and the product of Chl a and PAR. The calculated inventory of POC from such relationship was within ± 15% (1 s.d.) from the measured value.

Structure and evolution of the current sheet by multi-spacecraft observations

Abstract: On April 22, 1979, from 0840 to 1018 UT, ISEE 1, ISEE 2 and IMP 8 were all in or near the magnetotail current sheet at 17 Re, 16 Re and 35 Re respectively while ISEE 3 monitored the solar wind 206 Re upstream of the Earth. A global perspective of the four spacecraft observations and of the ground magnetic records is presented in this paper. The hyperbolic tangent current sheet model of Harris has been used to calculate the current sheet thickness and to analyze the plasma distribution in the vertical direction. It is found that during this event the current sheet thickness varied from 2.5 Re to 1.5 Re for northward IMF but thinned abruptly to 0.5 Re when the IMF turned southward.

Preliminary Result of Ocean Tide Estimation Over the Western Pacific Using Topex/Poseidon and ERS-1 Altimetry

Abstract: In this study, we attempted to determine the M 2 residual tide with respect to the CSR 3.0 tide model using TOPEX/POSEIDON (T/P) and ERS-1 altimeter data over the Western Pacific Region. The sea surface height (SSH) data were first crossover adjusted to remove biases in satellite orbit and then used to form the residual heights for the recovery of residual tide. Also, a theory of tidal error for averaged SSH was proposed, indicating that a 10 cm error in M 2 tide will be reduced to 0.41 cm for annually averaged T/P SSH and 0.87 cm for annually averaged ERS-1 SSH. The error theory also predicts that data averaging cannot reduce the error due to S 2 tide for the sun-synchronous ERS-1. With the error theory, we formed one mean surface from one year of T/P data and another from 1.5 years of ERS-1 data and the two mean sea surface were used separately as the reference surfaces for T/P and ERS-1. Moreover, a harmonic analysis method, in which the amplitude and phase were modeled by spherical harmonic expansions with transformed spherical coordinates, was adopted to estimate the residual M 2 tide. Analysis results indicate that the transformed spherical coordinates not only increase the spatial resolution of the “local” spherical harmonic expansions, but also help to avoid ill-conditioned systems in leastsquares. By using data from cycles 2 to 36 of T/P and data from cycles 6 to 15 of ERS-1, we tested with various expansion degrees for the residual M 2 recovery. The optimum result is the ERS-1 degree 20 solution which the size of the studied area (50° × 50°) has a spatial resolution of 1.25°. According to the comparison at selected tide gauge stations, the rms improvement to the CSR 3.0 tide from the ERS-1 degree 20 solution is 1.68 cm, i.e., better than the improvement obtained in other works.