Robert E. Crippen

Calculating the vegetation index faster

Abstract The near-infrared (NIR) versus red “infrared percentage vegetation index,” NIR /( NIR + Red ), is functionally and linearly equivalent to the normalized difference vegetation index, ( NIR - Red /( NIR + Red ). Advantageously, it is both computationally faster and never negative.

Middle Miocene extension in the Gulf Extensional Province, Baja California: Evidence from the southern Sierra Juarez

New geologic mapping, structural studies, and geochronology of Miocene volcanic and sedimentary rocks in the southern Sierra Juarez, Baja California, shed light on the extensional history of the Gulf Extensional Province prior to sea-floor spreading in the Gulf of California. The southern Sierra Juarez is underlain by lower–middle Miocene rocks including fluvial strata, intermediate composition volcanic deposits, basalt lava flows and cinder cones, and dacite pyroclastic deposits and lavas that nonconformably overlie the Cretaceous Peninsular Ranges batholith. The 40 Ar/ 39 Ar geochronology indicates that basaltic rocks are 16.90 ± 0.05 Ma and dacite pyroclastic deposits are between 16.69 ± 0.11 Ma and 15.98 ± 0.13 Ma. These strata were subsequently cut by two generations of faults. First generation faults comprise a dominant set of north-south–striking, west-dipping normal faults, a secondary set of north-south–striking, east-dipping normal faults, and a lesser set of variably oriented strike-slip faults. All three fault sets are temporally and spatially related and were produced by east-west extension. The dominant west-dipping faults, which are antithetic to and oblique to the east-dipping Main Gulf Escarpment, may have been a precursor or an early phase accommodation zone along the escarpment. West-dipping normal faults are cut by a 10.96 ± 0.05 Ma dacite hypabyssal intrusion, thus bracketing the age of east-west extension between 15.98 ± 0.13 Ma and 10.96 ± 0.05 Ma. Hence, this faulting event clearly indicates a period of extension that predates the onset of oceanic rifting and even predates other dated Miocene extension within Baja California. Second generation faults, which are comprised of east-west–striking strike-slip faults that cut first generation faults and associated northwest-striking, northeast-dipping normal faults, may be related to early development of the Transpeninsular Strike-slip Province. Global plate reconstructions suggest that transtensional motion between the North American and Pacific plates along the western margin of Baja California began during middle Miocene time, coeval with east-west extension in the southern Sierra Juarez. This observation supports a hypothesis that middle Miocene transtensional plate motion was partitioned into two components: a strike-slip component parallel to active faults along the western offshore margin of Baja California, and an extensional component normal to the margin, but located in what is now the Gulf Extensional Province. Hence, the onset of extension within the circum-gulf region was in response to plate boundary processes.

Measurement of Subresolution Terrain Displacements Using Spot Panchromatic Imagery

It is shown that satellite-derived imagery can be used to measure subresolution horizontal terrain displacements associated with present-day earthquakes, sand dune migration, glacial motion, coastal sediment transport, and pre-eruptive volcanic processes. This use of these data allows the detection of change and the determination of rates of many environmental processes worldwide. The premise of the method is that areally extensive, subresolution spatial differences in ground patterns between images acquired at different times can be accurately measured to high precision and can be distinguished from systematic image differences, such as those due to sensing-system attitude variations. Thus far, a preliminary algorithm has been tested that shows that the approach is reasonable.

The dangers of underestimating the importance of data adjustments in band ratioing

The practical importance of simple data adjustments for path (atmospheric) radiance and sensor calibration offsets prior to band ratioing has often been overlooked or misjudged. This paper describes and demonstrates the critical nature of data adjustments for the production of useful ratio images, including ratio images derived solely from long wavelength bands. A simple bispectral graphic model is used for illustrating and evaluating the impact of data offsets upon ratio images. Orthogonal indices, used as alternatives to band ratios, are shown to be sometimes less sensitive to topographic influences than ratios of unadjusted data but not less sensitive than ratios of properly adjusted data.

Directed band ratioing for the retention of perceptually-independent topographic expression in chromaticity-enhanced imagery

Abstract Enhancements of multispectral imagery, intended for visual interpretation of geological information, are typically designed to increase the discrimina-bility of band-variant surface reflectance features. Band ratioing has been commonly used for this purpose with various degrees of success. A disadvantage of band ratioing has been the loss of topographic expression and surface albedo information or, in some cases, the perceptual convolution of both topographic expression and albedo information with band-variant reflectance information. Topographic expression is a valuable indicator of structural and lithomorphic information and is typically the primary provider of reference landmarks. Albedo information is commonly critical in discriminating between some rock types. We have developed a method of band ratioing that directs the retention of topographic expression and albedo information so that they remain depicted as prominent variations in image intensity. The method involves adjusting the band dat...

Satellite Monitoring of Pakistan's Rockslide‐Dammed Lake Gojal

On 4 January 2010, a rockslide 1200 meters long, 350 meters wide, and 125 meters high dammed the Hunza River in Attabad, northern Pakistan, and formed Lake Gojal. The initial mass movement of rock killed 20 people and submerged several villages and 22 kilometers of the strategic Karakoram Highway linking Pakistan and China. Tens of thousands of people were displaced or cut off from overland connection with the rest of the country. On 29 May, the lake overflow began to pour through a spillway excavated by Pakistani authorities. On approximately 20 July, the lake attained a maximum depth of 119 meters and a torrent at least 9 meters deep issued over the spillway, according to Pakistans National Disaster Management Authority (NDMA). To date, the natural dam is holding and eroding slowly. However, the threat of a catastrophic outburst flood remains.

Recent changes in the snout position and surface velocity of Gangotri glacier observed from space

Glacier mass variations have a direct impact on some of the key components of the global water cycle, including sea level rise and freshwater availability. Apart from being one of the largest Himalayan glaciers, Gangotri is one of the sources of water for the Ganges river, which has a considerable influence on the socioeconomic structure of a largely over-populated catchment area accounting for ∼26% of India’s landmass. In this study, we present the most recent assessment of the Gangotri glacier dynamics, combining the use of interferometric techniques on synthetic aperture radar data and sub-pixel offset tracking on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery. Results show that on average, the Gangotri glacier snout has receded at a rate of 21.3 ± 3 m year−1 over a period of 6 years (2004–2010). While glacier surface velocity near the snout is estimated to be between 24.8 ± 2.3 and 28.9 ± 2.3 m year−1, interior portions of the glacier recorded velocities in the range of 13.9 ± 2.3 to 70.2 ± 2.3 m year−1. Further, the average glacier surface velocity in the northern (lower) portions (28.1 ± 2.3 m year−1) is observed to be significantly lower than in the southern (higher) portions (48.1 ± 2.3 m year−1) of the Gangotri glacier. These values are calculated with an uncertainty of less than 5 m year−1. Results also highlight a consistent retreat and non-uniform dynamics of the Gangotri glacier.

Using airborne and satellite data for multitemporal studies of land degradation

Remote sensing data collected from orbital satellites can provide global coverage at regular intervals at moderate to high spatial resolutions in broad spectral bands. Airborne instruments, such as the Jet Propulsion Laboratory Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS), can provide high spatial resolution in narrow spectral bands. High spectral resolution information is potentially useful for identifying and mapping such things as mineralogy and plant communities. However, airborne systems cannot easily provide periodic coverage nor can they provide global coverage of any sort. The logical outgrowth of this problem is to use airborne and satellite data synergistically. In this study, data from the AVIRIS airborne instrument, the Landsat MultiSpectral Scanner (MSS), and the ex-Soviet RESOURCE satellite have been combined into a co-registered temporal dataset covering the period from 1972 to 1991. The data cover the Manix Basin Area of the Mojave Desert, which is located NE of Barstow, California. This area has been cultivated with center-pivot irrigation systems. Beginning in 1973, a series of fields has been abandoned producing a sequence of abandoned fields at different stages of evolution. The remote sensing data shows that the vegetation cover on recently abandoned fields typically exceeds that in the surrounding desert for a few years. This is followed by a rapid decline in vegetation cover leading to the abandoned fields becoming more barren than the adjoining desert. The effects of wind erosion on vegetation cover can be easily seen in the temporal data The time series of data allows quantitative measurements of the area covered by active sand. On-site investigations have confirmed the relative barrenness of old abandoned fields and the relatively high vegetation cover on recently abandoned fields. Regions that have been identified in the remote sensing data as areas undergoing sand mobilization show evidence of wind erosion when observed on the ground. This study shows that the abandonment of irrigated fields in arid regions leads to land degradation which may not be evident from a single on-site or remote sensing observation.<<ETX>>

New perspectives on active tectonics: observing fault motion, mapping earthquake strain fields, and visualizing seismic events in multiple dimensions using satellite imagery and geophysical data bases

Remotely sensed imagery can be applied to neotectonic studies in ways quite different from its traditional use, the generation of enhanced spectral maps. Large neotectonic motions can be visually observed, seismogenic strain fields can be mapped, and the imagery can be combined with other geophysical data sets for synergistic, real-time exploration of multi-dimensional relationships.<<ETX>>

Color Composite Processing Of Multi-wavelength, Multi-polarization Airborne Radar Imagery

Multiwavelength, multipolarization radar image data can be processed to allow the clear depiction of most information in color composite displays. The first principal component, depicted as variations in image intensity, captures the dominant variation in the data and reduces noise without degradation of spatial detail. Other principal components, depicted primarily as variations in image chromaticity, are derived from spatially filtered data so that image colors can be attributed to significant wavelength and polarization contrasts, and not to speckle. Processing paths can be designed to emphasize wavelength contrasts, polarization contrasts, or overall discrimination of surface features.