Hiroki Motoyoshi

Variations of the snow physical parameters and their effects on albedo in Sapporo, Japan

Abstract Continuous measurements of the radiation budget and meteorological components, along with frequent snow-pit work, were performed in Sapporo, Hokkaido, Japan, during two winters from 2003 to 2005. The measured relationships between broadband albedos and the mass concentration of snow impurities were compared with theoretically predicted relationships calculated using a radiative transfer model for the atmosphere–snow system in which different types (in light absorption) of impurity models based on mineral dust and soot were assumed. The result suggests that the snow in Sapporo was contaminated not only with mineral dust but also with more absorptive soot. A comparison of the measured relationships between broadband albedos and snow grain size for two different layers with the theoretically predicted relationships revealed that the visible albedo contains information about the snow grain size in deeper snow layers (10 cm), and the near-infrared albedo contains only surface information. This is due to the difference in penetration depth of solar radiation into snow between the visible and the near-infrared wavelengths.

A satellite cross-calibration experiment

Recently, the Advanced Earth Observing Satellite 2 (ADEOS-2) was launched (December 14, 2002) successfully, and the Global Imager (GLI) onboard the ADEOS-2 satellite became operational in April 2003. In a first calibration checkup, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As a calibration site, a large snowfield near Barrow, Alaska, was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, the Moderate Resolution Imaging Spectroradiometer (Terra, Aqua), the Sea-viewing Wide Field-of-view Sensor, the Advanced Very High Resolution Radiometer (N16, N17), the Medium Resolution Imaging Spectrometer, and the Advanced Along Track Scanning Radiometer datasets were selected for the following clear-sky condition days: April 14 and 26, 2003. At the same time, ground-truth experiments (e.g., measurements of ground reflectance, bidirectional reflectance distribution function, aerosol optical thickness) were carried out. Thereinafter, top-of-atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code for each sensor, each band, and each day. Finally, the vicariously retrieved TOA signal was compared to TOA sensor Level 1B data. As a result, GLIs performance is encouraging at that time of the mission. GLI and the other seven sensors deliver similar sensor output in the range of about 5% to 7% around the expected vicariously calculated TOA signal.

Cross-calibration of satellite sensors over snow fields

Besides pre-launch and on-board calibration, the method of vicariously calibrating space sensors became a reliable tool for space sensor calibration. One possibility of vicarious calibration is to inter-calibrate sensors aboard different satellite platforms directly. This leads to a better understanding of differences in global data sets produced these sensors. Recently, ADEOS-2 was launched (14 Dec 2002) successfully and the optical sensor GLI onboard the ADEOS-2 satellite became operational from April 2003. In a first calibration check-up, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As calibration site a large snowfield near Barrow (Alaska, USA) was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, MODIS (terra, aqua), SeaWiFS, AHVRR (N16, N17) and MERIS data sets were selected for the following clear-sky condition days: April 14th and 26th 2003. At the same time ground-truth experiments, e.g., measurements of ground reflectance, BRDF, aerosol optical thickness (AOT), were carried out. Thereinafter, top-of-atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code (RTC) for each sensor, each band and each day. Finally, the vicariously retrieved TOA reflectance was compared to TOA sensor L1B data. As a result GLI’s performance is encouraging at this early time of the mission. GLI and the other 6 sensors deliver similar sensor output in the range of about 5-7% around the expected vicariously calculated TOA signal.

Empirical Relationships for Estimating Liquid Water Fraction of Melting Snowflakes

AbstractThe liquid water fraction of individual snowflakes f is an important parameter when calculating the radar reflectivity of a melting layer. A ground-based observation of f at Nagaoka, Japan, was conducted by using dye-treated filter papers that were kept at a temperature of 0°C. From the results of these measurements, which consisted of 6179 particles taken with 44 sheets of filter paper, two empirical relationships are proposed. The first is a relationship between the ratio of liquid water flux to total precipitation intensity (FL; taking values from 0 to 1) and meteorological surface data. The second is a relationship to estimate f using the melted diameter of a snowflake, median mass diameter, and FL. It was determined that the root-mean-square errors for estimating FL and f by using these relationships were 0.160 and 0.144, respectively. It was also found that the ratio of raindrop flux to the total precipitation intensity FR was always below 0.1 when FL was less than 0.6 but increased rapidly ...

Validation results of ADEOS-II/GLI snow products

Two types of snow grain sizes and mass concentration of snow impurities were made with ADEOS-II/GLI data from April to October in 2004. In general, both of retrieved snow parameters took lower values in the high latitudinal areas and low temperature areas. For the calibration of the sensor and the validation of the algorithms, several field campaigns were carried out in Alaska and eastern Hokkaido, Japan. Based on snow pit work, the retrieved snow grain size using the channel combination at 0.46μm and 0.865μm agreed with the measured values averaged over a snow layers from surface to several-cm depth. However, the satellitederived grain sizes from 1.64μm-channel, which is expected to be sensitive to surface snow grain size, were generally smaller than those measured at the ground. Possible reason of this underestimate is sun crust (thin ice layer created by solar radiation under clear sky) at snow surface, which increases the snow reflectance by additional specular reflection, in the case of granular (wet) snow during melting reason. The mass concentration of snow impurities retrieved from the satellite data was lower than the measured one. This is because snow impurities are assumed to be soot in the remote sensing algorithm, whereas the main composition of in situ measured impurities was generally found to be mineral dust in our sites.

Correction to “Influence of dust and black carbon on the snow albedo in the NASA Goddard Earth Observing System version 5 land surface model”

The website information describing the forcing meteorological data used for the land surface model (LSM) simulation, which were observed at an Automated Meteorological Station CAWS) at the Sapporo District Meteorological Observatory maintained by the Japan Meteorological Agency (JMA), was missing from the text. The 1-hourly data were obtained from the website of Kisyoutoukeijouhou (Information for available JMA-observed meteorological data in the past) on the website of JMA (in Japanese) (available at: http://www.jma.go.jpijmaimenulreport.html). The measurement height information of 59.5 m for the anemometer at the Sapporo Observatory was also obtained from the website of JMA (in Japanese) (available at: http://www.jma.go.jp/jma/menu/report.html). In addition, the converted 10-m wind speed, based on the AWS/JMA data, was further converted to a 2-m wind speed prior to its use with the land model as a usual treatment of off-line Catchment simulation. Please ignore the ice absorption data on the website mentioned in paragraph [15] which was not used for our calculations (but the data on the website was mostly the same as the estimated ice absorption coefficients by the following method because they partially used the same data by Warren [1984]). We calculated the ice absorption coefficients with the method mentioned in the same paragraph, for which some of the refractive index data by Warren [1984] were used and then interpolated between wavelengths, and also mentioned in paragraph [20] for the visible (VIS) and near-infrared (NIR) ranges. The optical data we used were interpolated between wavelengths as necessary.

GLI cryosphere products and validation

The Global Imager (GLI) aboard the ADEOS-II satellite launched in December 14, 2002 observed sunlight reflection and infrared emission from the Earths surface globally, and detected various geophysical parameters (e.g., snow and sea-ice cover extent, snow grain size and impurity). They contribute to the investigation of global hydrological cycle and radiation budget that are primal factors of the global climate change. Preliminary analysis results of the GLI snow products with 6-month GLI data and their validation results are presented.