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When a logic gate switches on, a signal is launched down the signal line, the current step i being taken from the positive supply line, and an equal and opposite current -i being dumped into the 0 V line at the point where the logic signal originated (see figure 7.1).

This subject is not a difficult one; indeed, the mathematics used is extremely elementary. The problems are caused rather by the historical progression from analog to digital techniques, with the consequent carrying over of well tried analog techniques into the digital environment. Unfortunately, the requirements for digital circuitry are frequently opposite to those needed by the analog variety, and hence there is a need for a complete reconsideration of the requirements.

In a digital system, sudden massive changes of load current in the power supply serving the logic can easily occur. For instance, it is not uncommon for a 32-bit word of data to be gated on to 32 parallel signal lines. If the word happens to be ‘all ones’, the amount of current suddenly switched out of the +5 V supply is quite large. For instance, if the lines are shunt terminated in their characteristic impedance of 100 Ω, the total current switched, at 50 mA per line for a 5 V signal, is 1.6 A. We see what a massive event this is when we assume a reasonable risetime for the signal, say 5 ns, and find that the rate of change of current out of the supply $$ \frac{{{d_i}}}{{{d_t}}} = \frac{{1.6}}{{5x{{10}^{ - 9}}}}A/s = 320x{10^6}\,A/s $$ For proper functioning of the logic it is important that such a massive, rapid current demand should not cause a significant drop in the voltage bus in the vicinity of the demand at any time after that demand has occurred. (A 50 mV drop could be regarded as the maximum acceptable.)

In this paper we examine the influence of a priori information on the roughness characteristics of agricultural fields within the context of soil moisture retrieval using SAR. Laser profile data from several European in-situ measurement campaigns is put together and typical distributions for 3 tillage types - seedbed, harrowed and ploughed - determined. In a subsequent step the information content and the retrieval uncertainties before and after a priori roughness information has been introduced into the inversion procedure is determined using a Bayesian approach.

Radar ice sounding allows for the retrieval of ice depth and provides information on ba-sal topography, basal conditions, flow, and layering. In the prospect of a possible future satellite ice sounding mission, surface clutters are expected to severely hamper measurement of radar ech-oes from the depth due to the unfavourable observation geometry. Synthetic aperture radar (SAR) processing enables to attenuate surface clutters in the forward and backward directions, but not in the across-track directions. Thus, additional across-track clutter cancellation is a crucial step for extracting weaker subsurface radar echoes. ESA’s P-band POLarimetric Airborne Radar Ice Sounder (POLARIS), recently upgraded with a larger antenna of 4 m length, enables simultaneous reception of up to 4 sub-aperture channels in across-track. Laboratory of Electromagnetics and Acoustics of Swiss Fed. Institute of Tech., Lausanne, developed and built the radiator-elements of the enhanced POLARIS. Several datasets were acquired in the multi-channel configuration during the Feb. 2011 campaign over East Antarctica. The POLARIS instrument will be briefly introduced, followed by an overview of the sounding campaign. Finally, different surface clutter suppression approaches, based on topographic data, are presented and compared. Clutter rejection performance is quantified through comparison with original data.

Russia's boreal forests host 11% of the world's live forest biomass. They play a critical role in Russia's economy and in stabilizing the global climate. The boreal forests of central and western Siberia represent the largest unbroken tracts of forest in the world. The European Commission funded SIBERIA project aimed at producing a forest map covering an area of 1.2 million square kilometres. Three synthetic aperture radars (SAR) on board the European remote sensing satellites ERS-1 and ERS-2 and the Japanese Earth resources satellite JERS-1 were used to collect remote sensing data. Radar is the only sensor capable of penetrating cloud cover and imaging at night. An adaptive, model-based, contextual classification to derive ranked total growing stock volume classes suitable for large-scale mapping is described. The accuracy assessment of the Siberian forest cover map is presented. The weighted coefficient of agreement κw is calculated to quantify the agreement between the classified map and the reference ...

In this paper, two model-based methods for soil moisture retrieval from SAR measurements are described. The performances of the two methods are compared using, simulated L-band data obtained by exploiting the integral equation model (IEM). The first method is based on a previously developed soil moisture retrieval algorithm. It estimates the soil moisture content by approximating the IEM inverse function using a neural network approach. The second method is an iterative technique which adopts a searching strategy by using the IEM direct model. The two methods are also compared when using a priori information, such as the roughness state of the bare soil surfaces.

In the framework of preparatory activities for the SPECTRA (Surface Processes and Ecosystems Changes Through Response Analysis) ESA Earth Explorer Core Mission, CHRIS/PROBA acquisitions over the Barrax Core Site in Spain were used to compile a reference dataset for future in-depth studies. Taking advantage of the possibility of consecutive days of acquisitions, multiple-angular acquisitions finally included 10 different view angles from CHRIS, in Mode 1 with 62 spectral, and a ground resolution of about 34 m. Additional ROSIS and HYMAP sensors, flying simultaneously with CHRIS overpass, provided detailed images for validation of CHRIS data, particularly in the spectral domain. Moreover, up to 3 angles per sample from airborne HYMAP data were acquired, with high spectral and spatial resolution, and then both spectral and angular domains can be exploited with the combined CHRIS/HYMAP/ROSIS dataset. Detailed soil/vegetation and atmospheric measurements complete the SPARC data, and data from other satellites (MERIS, SEVIRI, SPOT, Landsat) were collected as well, to address scaling issues. Methods for data analysis and exploitation have been developed in the context of SPARC activities, and preliminary results about retrievals of biophysical information from multi-angular hyperspectral data are already available. The whole SPARC dataset represents a reference for the exploitation of CHRIS data, allowing the development of new processing and retrieval algorithms, and the validation of such algorithms by means of ground measurements and complementary airborne and satellite data. More details on several processing aspects of the CHRIS/PROBA data acquired within the SPARC campaign are presented in other papers in this conference.

Quantifies penetration capabilities of radar systems in arid areas, for sub-surface imaging purposes. Data acquisition systems considered range from ground penetrating radars to airborne and orbital synthetic aperture radars. First fieldwork results are presented for two study sites: one is located in France (Pilat dune near Bordeaux) and the other one is located in East Africa (Republic of Djibouti). Data obtained are used to constrain theoretical radar backscattering models, including both surface and volume scattering terms.

After the successful launch of CryoSat-2 in April 2010, ESA has funded two validation campaigns (CryoSat Validation Experiment, CryoVEx) of the satellite in the Arctic regions in the spring of 2011 and 2012. The primary aim of the CryoVEx campaigns is to directly validate the measurements from CryoSat-2 by comparison to airborne and ground measurements. This is possible only through a major effort involving a large group of international partners. DTU Space has been involved in the CryoVEx campaigns with airborne activities since 2003. To validate the performance of the CryoSat-2 radar altimeter (SIRAL), the aircraft is equipped with an airborne version of the SIRAL altimeter (ASIRAS) together with a laser scanner.The campaigns are focused on five main validation sites: Devon ice cap (Canada), Austfonna ice cap (Svalbard), the EGIG line crossing the Greenland Ice Sheet, as well as the sea ice north of Alert and sea ice around Svalbard in the Fram Strait. Selected tracks were planned to match CryoSat-2 passes and a few of them were flown in formation flight with the Alfred Wegener Institute (AWI) Polar-5 carrying an EM-bird. This presentation summarizes the 2011-12 airborne campaigns in the Arctic region, and includes results of coincident CryoSat-2 (level 1b and 2) and airborne measurements.

Since the launch of ERS-1 in 1991, a number of studies have yielded experimental correlations between the observed radar backscatter and soil moisture prevalent at the time of the image acquisition. However at the same time these empirical results appear to be both site and time dependent and difficult to generalise unless the resolution is degraded in order to average out roughness influences. Surface roughness is known to play an important role in the scattering of electromagnetic waves from natural surfaces. The relative sensitivity of the radar backscatter to surface roughness compared to that of the soil moisture depends on the wave characteristics (frequency, polarisation, incidence) and on the geometric and dielectric properties of the soil surfaces.

The TropiSAR campaign has been conducted in August 2009 in French Guiana with the ONERA airborne system SETHI. The main objective of this campaign was to collect data to support the Phase A of the Earth Explorer candidate mission, Biomass. Several specific questions need to be addressed to answer the recommendations of the ESAC group and the data collection strategy has been constructed accordingly. The first part of the paper lists these specific questions. We then describe the selected test sites, followed by a summary on the radar instrument and the radar configuration (geometry and waveform). The data acquisition plan is provided and the first results conclude this paper.

After the successful launch of CryoSat-2 in April 2010, the first direct validation campaign of the satellite was carried out in the April-May 2011. DTU Space has been involved in ESA’s CryoSat Validation Experiment (CryoVEx) with airborne activities since 2003. To validate the performance of the CryoSat-2 radar altimeter (SIRAL), the aircraft is equipped with an airborne version of the SIRAL altimeter (ASIRAS) together with a laser scanner. Of particular interest is to study the penetration depth of SIRAL into both land- and sea ice. This can be done by comparing the radar and laser measurements, as the laser reflects on the surface, and by overflight of laser reflectors. In the spring of 2011 the DTU Space airborne team visited five main validation sites: Devon ice cap (Canada), Austfonna ice cap (Svalbard), the EGIG line crossing the Greenland Ice Sheet, as well as the sea ice north of Alert and sea ice around Svalbard in the Fram Strait. Selected tracks were planned to match CryoSat-2 passes and a few of them were flown in formation flight with the Alfred Wegener Institute (AWI) Polar-5 carrying an EM-bird. We present an overview of the 2011 airborne campaign together with first results of the CryoSat-2 underflights.

Ground and ERS SAR data acquired over bare soils located in The Netherlands, France and Italy are analysed. Correlation properties of long roughness profiles are shown. Besides, SAR data are compared with theoretical predictions and results are discussed by using simulated data obtained by exploiting a MOM code.

This paper describes the motivation behind and the characteristics of a laser profiler which has been specifically tailored to the measurement of surface roughness characteristics of importance in the radar electromagnetic scattering studies-and hence inversion and retrieval algorithms. The main feature of this profiler is its capability of recording roughness profiles at the scale of the spaceborne SAR resolution, which is roughly of the order of 25 meters for current radar satellites such as ERS-2 or RADARSAT.