OVERSEAS TRAVEL REPORT
Report Australian Activities to the CEOS WGCV#14
Ian Barton,
CSIRO Marine
Several new activities have been identified and these are treated with more detail.
Ongoing activities identified in the 1996/7 reports to WGCV12/13 are listed below. Note that details of all cal/val sites can be obtained from the CEOS Cal/val site dossier on the WWW:
I. Continued operation of the CSIRO CIGSN Calibration Sites, plus the development of a new sites at Tinga Tingana and Thangoo (a tropical site).
II. Altimeter validation.
III. AVHRR solar reflectance channels - Calibration info. on the WWW.
IV. Antarctic activities.
V. Ocean colour cal/val.
VI. POLDER validation campaign
VII. Validation of sea surface temperatures.
VIII. The CEOS IR Inter-comparison Pilot Program. Analysis of the data collected at Townsville during July 1997 continues. A presentation of preliminary results will be given to the 32nd COSPAR Scientific Assembly in Japan during July 1998.
NOTE: CSIRO continues to develop its validation plan for its NASA EOS activity through an Interdisciplinary Investigation entitled ``The Relationship between Climate, Ocean Circulation, Biological Processes, and Renewable Marine Resources''. Planning also continues for the validation and calibration of data from instruments on ENVISAT and ADEOS-II.
NEW ACTIVITIES
1. Lunar calibration of the GMS-5 VIS imager
Ian Grant, CSIRO Atmospheric Research, 26 June 1998
Visible-band imagers on geostationary satellites can potentially contribute a wealth of data on problems as diverse as surface radiation, aerosol distribution, biomass burning and vegetation state because they uniquely resolve diurnal cycles with near-global coverage. Accurate calibration of the GMS visible imager is necessary for quantitative applications of its images of Australia. The calibration of all visible-band satellite sensors is problematic and is usually done through campaigns of ground-based or airborne measurements of land targets. The moon is a potential alternative calibration target for monitoring the stability and measuring the absolute calibration of earth observing satellite sensors.
The advantages of lunar calibration:
A disadvantage:
A US Geological Survey (USGS) team (lead by Hugh Kieffer) is conducting a program of lunar photometry to establish the moon as a spectral radiance calibration target for EOS sensors. Since the moon sometimes appears in the corners of the GMS full-disk images of the earth, this new technique could, in principle, be applied to all archived and future GMS VIS-band images that include the moon. However, the calibration of an arbitrary image must wait for the completion of the USGS's four-year observation program, in order to have a sufficiently dense observational database to allow interpolation to an arbitrary viewing and illumination geometry. However, there are two narrow ranges of longitude from which a geostationary satellite can image the moon nearly simultaneously with, and from almost the same viewing direction as, USGS's observatory in Flagstaff, Arizona. GMS is in one of these ranges and Europe's Meteosat is in the other. This circumvents the need for interpolation and so allows an immediate calibration of GMS and an early demonstration of the lunar calibration technique in general.
The moon is favourably positioned in the operational GMS-5 image only a few times each year, and the sky over Flagstaff must be clear at the time of such an image to get data suitable for a calibration. The first suitable pair of images was acquired on 22 August 1997 (Figure: pair of images). After co-registration, and synthesis of the GMS VIS band from 6USGS narrow bands by spectral interpolation and integration, some preliminary comparisons have been made. (Figure: scatterplot with fitted curve.) The calibration of the USGS data is preliminary; final results expected within a few months.
This is a useful adjunct to the GMS Pathfinder team's more frequent cross-calibration of GMS with AVHRR on clouds. I have begun working with EUMETSAT scientists (Govaerts and Schmetz) to calibrate the European Meteosats; an opportunity in January was clouded out in Arizona.
Three figures are available on request.
1. Point list of advantages of lunar calibration
2. Image pair:
- USGS spectrally synthesised, not co-registered
- USGS calibration very preliminary so don't worry about units
- -GMS has square-root radiance scale, USGS linear
3. Calibration scatter plot for one GMS pixel
2. Earth Occultation Measurements from LEO Satellites in the Southern Hemisphere Using GPS and GLONASS
Mr Marceli Firlejczyk and Prof. Garth Morgan ACTE, University of South Australia, Adelaide
The planetary atmosphere occultation technique was successfully tested for the Earth's atmosphere in 1995 by the Microlab-1 satellite with a receiver modified to receive dual frequency signals from the GPS navigational satellite galaxy. The present paper proposes a receiver system for radio occultation measurements from both GPS and GLONASS galaxies. The principle involves accurately measuring arrival times of navigational signals at each occultation of a Low Earth Orbiting (LEO) receiver. Each transmission is retarded by refractive bending and delayed as it traverses the atmosphere and since the atmospheric refraction index is a function of the occultation altitude, atmospheric profiles of tropospheric pressure, temperature and water vapour, as well ionospheric free electron density, are able to be gathered continuously to provide a very large climatology database for meteorological, geodetic and communication users. Such a climatology is expected to be of paramount importance in monitoring the health of the Earth's atmosphere. This research reviews occultation measurement concepts for Earth atmospheric health monitoring and proposes improved modelling and validation of LEO satellite measurements by the rigorous ACTE T&E methodologies.
3. Miami Workshops during March 1998.
Ian Barton, CSIRO
Australian scientists participated in two workshops at Miami Uni.A round-robin infrared radiometer comparison and absolute calibration was undertaken. A workshop on international collaboration in the validation of infrared data products was also held. Details are available at http://www.rsmas.miami.edu/ir
4. Hillarys Cross-Shelf Transect, Perth, Western Australia
Merv Lynch, Curtin University
A monthly field survey being carried out off Hillarys Marina by CSIRO, Curtin University and the WA Fisheries Department. As part of a national study largely funded by the Fisheries Research and Development Corporation (FRDC), these monthly surveys have been undertaken since October 1996 to measure the physical, chemical and bio-optical properties of the continental shelf waters due west of Hillarys Marina just north of Perth. Present funding for the transects ends in December 1998, but means will be explored for continuing the measurements for at least another year if possible because of the ongoing need for satellite validation, as well as the intrinsic value of regular sampling across our continental shelf. The Perth Diving Academy vessel Lionfish II is chartered for the work, and we are indebted to the PDA for their helpful assistance each month.
The transects, which comprise both underway sampling and 9 profiling stations out to 40 km offshore, include temperature, salinity, chlorophyll, nutrients (nitrate, silicate and phosphorus), light measurements, and both phyto- and zoo-plankton trawls. These data are being used for surface validation of satellite measurements, specifically SeaWiFS-derived chlorophyll estimates (including the development/refinement of chlorophyll algorithms) and sea-surface temperatures from the NOAA/AVHRR and ATSR satellite sensors. The trigger for this study was the August 1997 launch of SeaWiFS, a satellite sensor designed to measure the colour of ocean waters and hence provide estimates of near-surface chlorophyll (and phytoplankton) concentrations. The Western Australian Satellite Technology and Applications Consortium (WASTAC) has a licence to receive SeaWiFS data in Perth; the other Australian receiving stations are CSIRO Marine Research in Hobart and the Australian Institute of Marine Science (AIMS) facility in Townsville.
During each monthly transect, sea-surface temperature, conductivity and fluorescence are sampled continuously both while the vessel is underway (on both the outward and return segments) as well as on station. At each of the9 stations, water temperatures are being measured in a variety of ways(simple bucket, floating near-surface loggers, a thermal infrared radiometer, and a profiling salinity-temperature-depth recorder) to study differences between "skin" (micro-surface layer) and "bulk" (sub surface)temperatures and their relationship with satellite-derived temperatures. Surface salinities are derived from bottle samples (subsequently analysed on a salinometer) and sub-surface salinities from the profiler. Simple wind and air temperature measurements are also made on each station. Light measurements comprise Secchi disc, Licor PAR sensor for vertical profiles, and Ocean Optics S1000 spectro-radiometer for downwelling irradiance, Chlorophyll fluorescence with a Biospherical INF300 instrument, water-leaving and sub-surface radiance. Depth-integrated chlorophyll and nutrient samples are taken on each station using a submersible pump system, and both phyto- and zooplankton net samples are taken as well.
4.1 Solar Photometer
The multi-filter rotating shadowband radiometer (MFR-7) from Yankee Environmental Systems has been operating atop the engineering building at Curtin since late December, 1997. This is presently being re-sited to an offshore location (Rottnest Island) for measuring marine aerosols.
4.2 Future Developments
Plans are in progress for Curtin University to deploy an ocean heat flux buoy and to simultaneously profile air temperature and moisture in the lower 10 to 15 meters of the maritime atmosphere as part of ocean heat flux research program. The intention is to use these data to evaluate the performance of algorithms for ocean heat flux estimation.
We are also developing (with University of WA) a solar photometer to operate in the 850 nm to 5 micron region to detect some of the larger maritime aerosols and to assess their radiative transfer consequences.
In association with Dr A J Prata CSIRO, a radiation research station is being established in Broome, Western Australia for satellite validation studies -for use with MODIS, ASTER, AATSR, AIRS.