Yuko Takeyama

Comparison of Geophysical Model Functions for SAR Wind Speed Retrieval in Japanese Coastal Waters

This work discusses the accuracies of geophysical model functions (GMFs) for retrieval of sea surface wind speed from satellite-borne Synthetic Aperture Radar (SAR) images in Japanese coastal waters characterized by short fetches and variable atmospheric stability conditions. In situ observations from two validation sites, Hiratsuka and Shirahama, are used for comparison of the retrieved sea surface wind speeds using CMOD (C-band model)4, CMOD_IFR2, CMOD5 and CMOD5.N. Of all the geophysical model functions (GMFs), the latest C-band GMF, CMOD5.N, has the smallest bias and root mean square error at both sites. All of the GMFs exhibit a negative bias in the retrieved wind speed. In order to understand the reason for this bias, all SAR-retrieved wind speeds are separated into two categories: onshore wind (blowing from sea to land) and offshore wind (blowing from land to sea). Only offshore winds were found to exhibit the large negative bias, and short fetches from the coastline may be a possible reason for this. Moreover, it is clarified that in both the unstable and stable conditions, CMOD5.N has atmospheric stability effectiveness, and can keep the same accuracy with CMOD5 in the neutral condition. In short, at the moment, CMOD5.N is thought to be the most promising GMF for the SAR wind speed retrieval with the atmospheric stability correction in Japanese coastal waters, although there is ample room for future improvement for the effect from short fetch.

Estimation of Offshore Wind Resources in Coastal Waters off Shirahama Using ENVISAT ASAR Images

Offshore wind resource maps for the coastal waters off Shirahama, Japan were made based on 104 images of the Advanced Synthetic Aperture Radar (ASAR) onboard the ENVISAT satellite. Wind speed fields were derived from the SAR images with the geophysical model function CMOD5.N. Mean wind speed and energy density were estimated using the Weibull distribution function. These accuracies were examined in comparison with in situ measurements from the Shirahama offshore platform and the Southwest Wakayama buoy (SW-buoy). Firstly, it was found that the SAR-derived 10 m-height wind speed had a bias of 0.52 m/s and a RMSE of 2.33 m/s at Shirahama. Secondly, it was found that the mean wind speeds estimated from SAR images and the Weibull distribution function were overestimated at both sites. The ratio between SAR-derived and in situ measured mean wind speeds at Shirahama is 1.07, and this value was used for a long-term bias correction in the SAR-derived wind speed. Finally, mean wind speed and wind energy density maps at 80 m height were made based on the corrected SAR-derived 10 m-height wind speeds and the ratio U80/U10 calculated from the mesoscale meteorological model WRF.

Development of ALOS/PALSAR data on-demand processing and providing system on GEO Grid

GEO Grid has been proposed by AIST in order to contribute to earth science.?? GEO Grid mainly provides satellite and field observation data related to earth science through data search service, data processing service and data providing service. Recently, we have developed ALOS PALSAR data on-demand processing and providing system as one of GEO Grid data providing system. The system allows users to easily search and quickly receive PALSAR products without careful considerations and advanced skills. There are two important points in the system. One is seamless connection between AIST and an external archive system. The other is that the system can provided calibrated PALSAR products according to observations using Corner Reflectors. As a future plan, OGC-CSW is applied to this system for data search service.

Study on Absolute Calibration Coefficient Improvement for ALOS PALSAR Data after Initial Calibration Check

The Advanced Land Observing Satellite (ALOS) was launched in 2006, carrying the Phased Array type L-band Synthetic Aperture Radar (PALSAR). Although three years have passed from the start of ALOS PALSAR observation, we know the PALSAR is in operation with greatly stability operation. However, we need to monitor its performance for the future sustainable operation in order to evaluate the temporal sensitivity variations of the PALSAR sensor and keep the calibration coe-cient quality and its improvement. To achieve this goal, AIST (National Institute of Advanced Industrial Science and Technology) kicked ofi the PALSAR calibration and validation campaign in 2007. We especially focus on cross-polarization calibration and aim to propose an improved backscattering coe-cient by evaluating the absolute calibration coe-cient accuracy is evaluated, which is calculated for each polarization based on the ground- truth. In the calibration observations, we used two triangular trihedral corner re∞ectors (CRs) of size 2m and 3m for the like-polarization and our inbuilt prototype rotatable rectangular dihedral CR was used for the cross-polarization.

Investigation of the Fetch Effect Using Onshore and Offshore Vertical LiDAR Devices

An offshore wind measurement campaign using vertical light detection and ranging (LiDAR) devices was conducted at the Hazaki Oceanographic Research Station (HORS) as part of an investigation into determining the optimal distance from the coast for a nearshore wind farm from a meteorological perspective. The research platform was a 427 m long pier located on a rectilinear coastline on the Pacific coast of the central Honshu Island in Japan. The relationship between the ratios of the increase of wind speed near the surface and fetch length within 5 km of the coast was analyzed via LiDAR observations taken at heights from 40 to 200 m. The results showed that the speed of the coastal wind blowing from land to sea gradually increased as the fetch length increased, by approximately 15–20% at 50 m above sea level around a fetch length of 2 km. Moreover, empirical equations were derived by applying the power law to the relationship between the increase of wind speed and fetch lengths at 1–5 km, as obtained from the LiDAR measurements. It was also found that the wind speed increase at a 2 km fetch length was equivalent to the effect of a 50–90 m vertical height increase on the coast in this region.