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Op e n-Fi le Re p o rt 82-6 7 5 M ultispe c tral images of an area near Marysvale, Utah , we r :! co llected by usi ng t he airborne U.S. National Aeron a utics a nd Space Administration (NASA) 24-c hannel Bendix multis pectral scanner; they were analyzed t o define areas of hy drothermall y altered, potentiall y mineralized rocks. Hydrothermally altered rocks, particularly volcan.tc rocks af f ected by solutions rich 1n sulfuric acid, are commonly characterized by concentrations of argillic minerals such as alunite and kaolinite. These minerals are important for identify ing hydrothermally altered rocks 1n multispectral images because they have an intense abso rption band cent ered near a wavelength of 2.2 um. Unaltered vo lcanic rocks commonl y lack these minerals and he nce co (I.ot have the absorption band. limonitic mine rals, such as goethite, hematite, jarosite, and. lepi do c rqcite a lso are c ommonl y associated with these deposits as a result of pri mar y and secondary processes. However, limonite al s o is widespread on unaltered rocks and is not abundant on some altered rocks in the s tudy area. Of the mi nerals me ntioned above, alunite is the only mineral in the are a 5 tudied t ha t is a \.OIliq ue produc t of hydrothermal precesses. equivalents of those in the thematic Mapper, a mult1spect!."al ::;canner to he launched on the Landsat-D satellite in 1982. These t:echniques, along wi t h the Thematic Mapper bands, should provide a rapid and more accurate means o f defining hydrothermally Ciltered areas than is possible by using the present Landsat multispectral scanner data. Introduct ion The M arysvale, Utah, area is located within a large volcanic field, and at many localities, the volcanic rocks have been altered by acidic hyd!."othermal solutions. Some of these altered areas contain economic mineral deposits that have sparked several mining booms in t ;,e region. Precious metals were exploited in the 1800 ' •• alunite during World Wars I and II. and uranium from the late 1940's to the 1960's. Cunningham and Steven (1979) ha'/e suggested that a potential for buried ""rphyry Clolybdenum deposits exists in this regio:J.. This paper describes some preliminary analytical results obtained utilizing aircraft multispectral scanner images for the detection of hydrothermally altered rocks in the Marysvale regio n. The techniques use bands 1n the visible and near-infrared portion of the electromagnetic spectrum that approximate toose of the Thematic Mapper multispectral scanner scheciuled ffjr launch on the Landsat-D satellite in 1982. Results indicate the techniques can: 1) distinguish readily between altered and unaltered volcanic rocks. n recognize areas of hydrothermally altered rocks not previ.ously oapped, and 3) disticguish different types of altered rocks.

Examination of SEASAT SAR images of eastern Maryland and Virginia reveals botanical distinctions between vegetated lowland areas and adjacent upland areas. Radar returns from the lowland areas can be either brighter or darker than returns from the upland forests. Scattering models and scatterometer measurements predict an increase of 6 dB in backscatter from vegetation over standing water. This agrees with the SCWigital number (DN) increase observed in the digital SEASAT data. The brightest areas in the Chickahominy, Virginia, drainage, containing P. virginica about 0.4 m high, contrast with the brightest areas in the Blackwater, Maryland, marshes, which contain mature loblolly pine in standing water. The darkest vegetated area in the Chickahominy drainage contains a forest of Nyssa aquatica (water tupelo) about 18 m high, while the darkest vegetated area in the Blackwater marshes contains the marsh plant Spartina alterniflora, 0.3 m high. The density, morphology, and relative geometry of the lowland vegetation with respect to standing water can all affect the strength of the return L band signal.

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