Ground Truth Data Collection Research Articles

Relationship among the surface albedo, spectral reflectance of canopy, and evaporative fraction at grassland and paddy field

Abstract For the purpose of estimating land surface fluxes over a large area, use of remote sensing techniques is and will be essential. Particularly, “ in situ ” collection of ground truth data has been a very important task for the development of satellite oriented “ algorithms ”. In this study, we observed “a patch scale” visible and near infrared spectral reflectance, which is obtainable from satellites, and land surface fluxes during and post-growing season at grassland and paddy field: Seasonal trends at grassland and at paddy field were quite different, because of the differences in water as well as growing environment. A good direct correlation was found between vegetation index (NDVI) and surface resistance during the growing season at grassland. A similar result was confirmed between NDVI and surface resistance at paddy field.

X-band SAR and scatterometer data inversion based on geometrical optics model and Kalman filter approach

This paper describes the activity performed in the framework of the 1990 AVIOSAR 580 SAR and scatterometer Italian campaign over the Matera test site. The experiment has been carried out to ascertain the reliability of surface scattering models in order to tackle with the data inversion problem. To achieve this goal, physical and geometrical features of 38 homogeneous bare soil fields are considered as a result of ground truth data collection. X band - VV polarization σ° values from the HUTSCAT scatterometer at 45° and from the CCRS airborne SAR sensor at the incidence angles between 50° and 62° are compared with those obtained from modeled data. The SAR data have been calibrated using both corner reflectors and extended natural targets. The backscatter variability due to surface roughness has been analyzed. Due to the characteristics of the analyzed data set, i.e., high incidence angle and surfaces with large root mean square slope profile m, the SPM and PO models were not suitable for many fields in the scene; on the other hand, a good agreement between theoretical predictions and experimental data is found when the Geometrical Optics (GO) model is used. A threshold value for m as function of the incidence angle is found and a physical interpretation of this behavior is also proposed. After the assessment of the GO model results, the problem of retrieving the real part of the soil relative dielectric constant Re(∈r) and m value is addressed as well, considering the extended Kalman filter approach. The comparison between the obtained values and the experimental data shows the reliability of the inversion approach, thus encouraging the use of more sophisticated backscattering models.

Design and development of a spectro-polarimeter for ground truth data collection

Abstract A spectro-polarimeter operating in ten spectral bands in the visible and near-IR range has been designed and developed for the measurement of Stokes parameters of reflected radiation from the terrain surfaces under in situ conditions. The radiometric performance and the data quality of the unit have been evaluated and explained. The instrument was extensively used in the field for the collection of spectral signatures of wheat canopies. The unit was also used in the laboratory. All spectral bands were found to be useful for the measurement of absolute values of spectral irradiance and spectral radiance, while bands 1-8 were found to be useful for the measurement of polarization. This article describes the design features and specifications and gives a typical set of field observations.

90° South: Antarctic expedition 1986–87

AbstractIn the austral summer 1986–87, the 75th anniversary of Amundsen's conquest of the South Pole, a sledging party of four from a private expedition, 90° South, set out to retrace his route. This was the culmination of five years of preparations, in which sufficient international support was raised to enable the expedition to reach Antarctica and operate independently, using its own ship, MV Aurora… The expedition's Twin Otter aircraft, flying from New Zealand, staged a unique refuelling operation on an iceberg within the pack ice 160 km from the Balleny Islands. Establishing a temporary base at Bay of Whales, Ross Ice Shelf, on 5 December 1986, the expedition used its aircraft to set up supply depots 220 km apart along the route to the pole. The sledging party with two teams of Greenland huskies crossed the ice shelf and ascended the Axel Heiberg Glacier to the polar plateau, reaching their fourth depot in 86°S in late January. Some 400 km short of the Pole, lack of time compelled the party to return to rendezvous with the ship. Glaciological investigations included the formation of icebergs from the Ross Ice Shelf, and collection of ground truth data to help in evaluating remote sensing data. The team also set up a commemorative plaque close to Amundsen' s cairn on Mount Betty.

Abundance Estimation of a Dispersed, Dynamic Population: Hooded Seals (Cystophora cristata) in the Northwest Atlantic

Pup production of hooded seals (Cystophora cristata) in the Northwest Atlantic was estimated by aerial survey. Simultaneous surveys and the collection of ground-truth data were conducted in March 1984 in both major whelping areas, namely the floe ice in the Davis Strait and off northeastern Newfoundland (the Front). Abundance estimates were obtained from both fixed-wing photographic and helicopter sighting surveys using a strip survey method for unequal-sized sampling units. These abundance estimates were corrected to account for pups which had left the ice and those pups which had yet to be born in each area. A maximum likelihood method was used to combine estimates of abundance from several surveys with estimates of the number of pups in each developmental stage to obtain an estimate of total production. This method weighted each survey point estimate of abundance by the estimated sampling variance and each estimate of the proportion of pups on the ice in each stage by the sample size corrected for loss of degrees of freedom associated with the sampling design. Total production at the Front was estimated to be 62 400 with 95% confidence limits of 43 700 to 89 400 and in the Davis Strait was 19 000 with a 95% confidence interval of 14 000 to 23 000. Total pup production estimates for the Front and Davis Strait are likely underestimates for several reasons, but are substantially higher than those previously assumed for the Northwest Atlantic.

Spectralradiometry and caribou range classification

The utility of Landsat in caribou range studies has been limited by problems of heterogeneity in cover type at the scale of pixies and by logistic barriers to ground truthing. Spectralradiometry provides an economical way of collecting ground truth data that are precisely comparable with Landsat data and which could provide a basis for hierarchic key classification rather than classification based on prinicipal components analysis. Spectral curves are presented for six common cover types and it is shown how the information could be used to develop classification criteria. Airborne data which could have provided a direct comparison with Landsat data proved to be too highly variable because of equipment constraints but there do not appear to be any significant barriers to developing the technique.

Surface Soil Water Content Measurement Using Pulsed Nuclear Magnetic Resonance Techniques

AbstractA tractor‐mounted pulsed nuclear magnetic resonance (NMR) moisture measurement instrument has been developed and fabricated for use in collecting ground truth data for calibrating and evaluating remotely sensed determinations. The measurement approach is based upon NMR which depends on the interaction between hydrogen nuclear magnetic moments and a magnetic field. The sensor unit, consisting of an electromagnet, detection coil, and tuning capacitor, is towed behind the tractor and provides continuous readout of the volumetric soil water content at selected depths to 63 mm. Preliminary laboratory measurements with this instrument on two soils, a clay and a loamy fine sand, correlate linearly with volumetric soil water content. Discrimination of water NMR signals from signals from other hydrogen‐bearing material is based on nuclear relaxation times, which reflect the molecular environment and structural bonding characteristics of the water molecules in the soil.

Potential applications of remote sensing techniques for the study of marine oil pollution

The detection and measurement of oil pollution in the marine environment are procedures requiring a broad range of instrumentation capabilities within an equally broad range of environmental conditions. Due to the complex behavior of oil on water, its susceptibility to transport and modification forces, and the physiochemical anomalies associated with its presence, both aerial and surface sensors are necessary to establish a complete and effective monitoring system. Remote sensors, operating in the ultraviolet, thermal infrared, and microwave portions of the electromagnetic spectrum, exhibit potentially good oil detection capabilities. Radar, in particular, possesses a strong capability for the mapping of an oil slick's areal extent since it is operative even under adverse weather conditions, day or night. Since no remote sensor system is presently capable of providing accurate information on the type or thickness of an oil slick, surface-based mechanisms must be utilized to gather ground truth data. These measurements, including the collection of radiometric, meteorological, and oceanographic information, are essential for a comparative analysis of remotely sensed data and their interpretation. More research is needed in the realm of remote sensing and ground truth data collection systems, including their coordination, if an operationally feasible system for monitoring marine oil pollution is to be developed.