Observations of Arctic Sea Ice Dynamics Using the Earth Resources Technology Satellite (ERTS-1)

This study shows that ERTS-l, launched by the U.S. National Aeronautics and Space Administration in July 1972, can be used to make synoptic observations of dynamic changes in arctic sea ice .... Each data swath of ERTS-l is 185 kilometres wide at the surface and is repeated once every 18 days. ... Because of a near-polar orbit, this sidelap increases to over 80 per cent at arctic latitudes. As a consequence of this large sidelap, the tracking of individual ice features for periods up to 5 or 6 days is permitted. The ERTS-1 Multispectral Scanner Subsystem (MSS) records data by simultaneously scanning across the satellite track in 4 spectral bands. The wavelength limits of the 4 bands are: green (0.5-0.6 µm), red (0.6-0.7 µm), and two near infrared bands (0.7-0.8 µm and 0.8-1.1 µm). The nominal spatial resolution for all 4 bands is 80 metres. A standard ERTS-1 photographic format has an image scale of nearly 1:1,000,000, which is convenient for direct comparison with available maps. Hendriksen Strait, the passage between Amund Ringnes Island and Cornwall Island at about 77°45' N and 95°00' W constituted the study area; it is in the Queen Elizabeth Islands of Arctic Canada, and is one of the most enticing and promising areas of recent oil and gas strikes. ... during a 6-day period from 23 to 28 August, ERTS-1 provided 5 days of coverage of Hendriksen Strait. Various types of sea ice can be identified in the ERTS-l imagery (0.6-0.7 µm band) .... In such a sequence of observations, a number of sea ice changes with time are detectable. Changes in position of individual ice floes can easily be translated to velocity. A number of ice floes were tracked over the 5-day period and their velocities calculated. The average velocity for ice floe movement was 8.5 kilometres/day .... ERTS-l can be used to study ice floe morphology and dynamics in the Beaufort Sea at time scales of several days to months. Repeated observations of individual ice floes such as those available here will also allow calculation of the ablation of the ice mass, in this case the decrease of surface area with time. ... The ice cover, i.e. the relative amount of sea ice present in a given area, is important for shipping purposes and air-sea interaction processes. The ice cover in Hendriksen Strait on 23 August was approximately 7/10, decreasing to 2/10 by 28 August. This type of sea ice change is easily observed from ERTS-1 .... In regard to the delineation of navigation routes through sea ice, the detection of active melting on the surface of the ice would indicate areas likely to be ice free in the near future. ERTS-1 has the ability to do this through observations of reflectance variability both temporally and spectrally. The second method of observing the sea ice reflectance change is provided by comparing two separate images made at the same time but in different spectral bands. ... Because the absorption of solar radiation by water is much greater in the near infrared than in the visible portion of the spectrum, the lower reflectance is again probably due to the presence of melt-water on the surface of the ice. Thus sea ice with water on it, even in very thin layers, will show a considerable difference in reflectance between these spectral bands of observation. ... Temporal and spectral observations of reflectance variations afforded by ERTS-l thus make it possible to locate areas of sea ice that are in varying stages of melting and breakup. The results presented here demonstrate that for high latitudes, ERTS-1 will provide overlapping coverage on sequential days that will allow observation of dynamic changes in the polar regions. In addition, route planning for shipping in the Arctic should benefit from frequent observations of sea ice movement and reflectance variations of the type obtainable from ERTS-l. Projected further, sea ice observations from ERTS-l over a period of years in the Arctic Islands should aid in the placement of offshore oil-drilling structures. Reflectance measurements over this period will also increase our understanding of the heat balance in the polar regions. Finally, ERTS-l observations of the amount of ice cover versus the amount of open water will be important in determining boundary conditions for future use in models of the global heat balance

Comparison of Precipitation Catch Between Nine Measuring Systems

A site was established by the United States Department of Agriculture-Agricultural Research Service on the Reynolds Creek Experimental Watershed in southwest Idaho in the fall of 1987 and operated through the spring of 1994, to compare precipitation catch between nine precipitation-measuring systems. This site was established as a part of the World Meteorological Organization’s program to compare current national methods of measuring solid precipitation (snow), so the primary emphasis of this study was the measurement of snowfall. Over seven seasons, four of the systems measured snowfall and total catch, which included snow, mixed snow and rain, and rain events, within 4% of the Wyoming shielded gauge, which had the greatest total catch. These measuring systems were the Alter shielded gauge and the dual-gauge system from the United States, the double-fence shielded gauge from Russia, and the Nipher shielded gauge from Canada. The unshielded universal recording gauge that was mounted with its orifice at 3.05 m had the least catch in all precipitation categories, which amounted to 24% less snow, 18% less mixed snow and rain, and 10% less rain than was measured by the Wyoming shielded gauge

Multi-Angle Data from CHRIS/Prob: a for Determination of Canopy Structure in Desert Rangelands

Multi-angle spectral radiance images from the Compact High Resolution Imaging Spectrometer (CHRIS) on the European Space Agency\u27s Proba satellite were acquired over desert grasslands in the USDA, ARS Jornada Experimental Range near Las Cruces, New Mexico, USA. The data were used to obtain multi-angle ratio images and to effect spatial bidirectional reflectance distribution function (BRDF) model inversions. The results show that there is canopy 3-D structure information observable in ratio images but physical interpretation is difficult. Inversion of a simple non-linear model for three canopy parameters resulted in low root-mean-square error values. The difficulty of decomposing the effects of brightness and reflectance anisotropy (BRDF shape) in complex desert shrub landscapes with varying soil-understory characteristics was overcome by allowing linear scaling of the parameters of the soil-understory sub-model as a function of near-nadir 631 nm reflectance. The retrieved parameter maps show a high spatial correlation between width and height but a different distribution for density. Examination of high resolution panchromatic and multi-spectral imagery shows that there are strong relationships between the retrieved parameters and canopy characteristics although further validation is required

Exploitation of Multi-Angle Data from CHRIS on PROBA: First Results from the Jornada Experimental Range

This study reports on work to assess the utility of multi-angle data in providing measures of the physical structure and composition of desert grasslands. The target is in the United State Department of Agriculture (USDA), Agricultural Research Service (ARS) Jornada Experimental Range (JER) near Las Cruces, New Mexico, USA. The JER is a CHRIS/Proba Core Site. The approaches followed include multi-angle image ratios, bi-directional reflectance distribution function (BRDF) model inversion - Li-Ross kernel-driven and the non-linear simple geometric model (SGM) - and the structural scattering index (SSI). The data used are from the Compact High Resolution Imaging Spectrometer (CHRIS) flown on the European Space Agency\u27s Project for On-Board Autonomy (Proba) satellite launched on October 22, 2001 into a sunsynchronous elliptical low Earth orbit. The results indicate that there is canopy structure information in angular ratio images, where spatial variation corresponds with mean plant size. The SSI did not behave as expected with high values corresponding to sparsely vegetated areas. SGM fits to data were good (mode RMSE \u3c 0.01) and produced mostly reasonable parameter values with meaningful spatial distributions

Improved Semi-Arid Community Type Differentiation with the NOAA AVHRR Via Exploitation of the Directional Signal

Mapping semi-arid vegetation types at the community level is extremely difficult for optical sensors with large ground footprints such as the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR). Attempts to usc solar wavelength AVHRR data in community type differentiation have often resulted in unacceptable classification errors which are usually attributed to noise from topographic and soil background variations, inaccurate reflectance retrieval and poor registration. One source of variation which is rarely accounted for adequately is the directional signal resulting from the combined effects of the surface bidirectional reflectance distribution function (BRDF) and the variation of viewing and illumination geometry as a function of scan angle, season, latitude and orbital overpass time. In this study, a linear semiempirical kernel-driven (LiSK) BRDF model is used to examine the utility of the directional signal in community and cover type differentiation over discontinuous but statistically homogeneous semi-arid canopies in Inner Mongolia Autonomous Region (IMAR), China, and New Mexico (NM), USA. This research shows that the directional signal resulting from the physical structure of the canopy-soil complex can be retrieved to provide information which is highly complementary to that obtained in the spectral domain