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The growing importance of polarimetric radiometers has led to the need for a detailed theory for Stokes antenna temperatures. In this paper, we provide a full Stokes vector formulation of an antenna temperature that accounts for the entire antenna pattern, which includes polarization mixing in the main-beam and sidelobe effects. To derive the Stokes antenna temperatures, we follow the conventional methods in the Earth remote sensing literature while relying on a coherency algebra approach from radio astronomy. Connections and parallels to the conventional approaches are noted along the way. We also introduce generalizations of beam efficiency and cross polarization for use with polarimetric radiometers. These provide important metrics in the design of future systems. Index Terms--Jones matrix, Mueller matrix, polarimetry, polarization, radiometry, Stokes parameters.

Methods are developed and evaluated to retrieve surface soil temperature information for the Advanced Microwave Scanning Radiometer on Earth Observing System for seven boreal forest and Arctic tundra biophysical monitoring sites across Alaska and Northern Canada. A multiple-band iterative radiative transfer process-based method producing dynamic vegetation and snow cover correction quantities and an empirical multiple regression method using several frequencies are employed. The seasonal pattern of microwave emission and relative accuracy of the soil temperature retrievals are influenced strongly by landscape properties, including the presence of open water, vegetation type and seasonal phenology, snow cover, and freeze-thaw transitions. The retrieval of soil temperature is similar for the two methods with an overall root-mean-square error of 3.1-3.9 K during summer thawed conditions, with a larger error occurring in winter during periods of dynamic snow cover and freeze--thaw state. These results indicate that at high latitudes, the influence of the atmosphere may be less important than that of surface conditions in determining the relative accuracy of the estimated soil temperature. Impacts of surface conditions on surface emissivity, observed brightness temperature, and estimated soil temperature are discussed. Index Terms--Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), Arctic tundra, boreal forest, microwave radiometry, satellite remote sensing, soil temperature.

An observing system simulation experiment is developed to test tradeoffs in resolution and accuracy for soil moisture estimation using active and passive L-band remote sensing. Concepts for combined radar and radiometer missions include designs that will provide multiresolution measurements. In this paper, the scientific impacts of instrument performance are analyzed to determine the measurement requirements for the mission concept. The ensemble Kalman smoother (EnKS) is used to merge these multiresolution observations with modeled soil moisture from a land surface model to estimate surface and subsurface soil moisture at 6-km resolution. The model used for assimilation is different from that used to generate 'truth.' Consequently, this experiment simulates how data assimilation performs in real applications when the model is not a perfect representation of reality. The EnKS is an extension of the ensemble Kalman filter (EnKF) in which observations are used to update states at previous times. Previous work demonstrated that it provides a computationally inexpensive means to improve the results from the EnKF, and that the limited memory in soil moisture can be exploited by employing it as a fixed lag smoother. Here, it is shown that the EnKS can be used in large problems with spatially distributed state vectors and spatially distributed multiresolution observations. The EnKS-based data assimilation framework is used to study the synergy between passive and active observations that have different resolutions and measurement error distributions. The extent to which the design parameters of the EnKS vary depending on the combination of observations assimilated is investigated. Index Terms--Data assimilation, ensemble Kalman filter, ensemble Kalman smoother, hydrology, land surface hydrology, microwave remote sensing, reanalysis, soil moisture.

Soil Moisture Experiment 2003 (SMEX03) was the second in a series of field campaigns using the National Oceanic and Atmospheric Administration Polarimetric Scanning Radiometer (PSR/CX) designed to validate brightness temperature ([T.sub.B]) data and soil moisture retrieval algorithms for the Advanced Microwave Scanning Radiometer (AMSR-E) for the Earth Observing System on the Aqua satellite. Objectives related to the PSR/CX during SMEX03 included: calibration and validation of AMSR-E [T.sub.B] observations over different climate/vegetation regions of the U.S. [Alabama (AL), Georgia (GA), Oklahoma (OK)], identification of possible areas of radio-frequency interference (RFI), comparison of X-band observations from Tropical Rainfall Measurement Mission Microwave Imager (TMI), AMSR-E, and PSR/CX, and exploring the potential of soil moisture retrieval algorithms using C- and X-band imagery in diverse landscapes. In the current investigation, more than 100 flightlines of PSR/CX data were extensively processed to produce gridded [T.sub.B] products for the four study regions. Due to the lack of significant rainfall in OK, generally dry soil moisture conditions were observed. Observations obtained over AL include a wide range of soil moisture and vegetation conditions. Results from the AL site clearly showed a lack of sensitivity to rainfall/soil moisture under forest canopy cover. Quantitative comparisons made with the TMI validated that both the PSR/CX and AMSR-E X-band channels were well calibrated. Spectral analyses indicated that the PSR/CX observations at C-band also are reasonable. As expected, there were varying degrees of RFI in the AMSR-E C-band data for the study sites that will prevent further soil moisture analysis using these data. X-band comparisons of the PSR/CX high-resolution and AMSR-E and TMI low-resolution data indicated a linear scaling for the range of conditions studied in SMEX03. These results will form the basis for further soil moisture investigations. Index Terms--Advanced Microwave Scanning Radiometer (AMSR-E), passive microwave, soil moisture, validation.

A new physically based disaggregation method is developed to improve the spatial resolution of the surface soil moisture extracted from the Soil Moisture and Ocean Salinity (SMOS) data. The approach combines the 40-km resolution SMOS multiangular brightness temperatures and 1-km resolution auxiliary data composed of visible, near-infrared, and thermal infrared remote sensing data and all the surface variables involved in the modeling of land surface-atmosphere interaction available at this scale (soil texture, atmospheric forcing, etc.). The method successively estimates a relative spatial distribution of soil moisture with fine-scale auxiliary data, and normalizes this distribution at SMOS resolution with SMOS data. The main assumption relies on the relationship between the radiometric soil temperature inverted from the thermal infrared and the microwave soil moisture. Based on synthetic data generated with a land surface model, it is shown that the radiometric soil temperature can be used as a tracer of the spatial variability of the 0-5 cm soil moisture. A sensitivity analysis shows that the algorithm remains stable for big uncertainties in auxiliary data and that the uncertainty in SMOS observation seems to be the limiting factor. Finally, a simple application to the SGP97/AVHRR data illustrates the usefulness of the approach. Index Terms--Disaggregation, multispectral remote sensing, Soil Moisture and Ocean Salinity (SMOS) mission, surface soil moisture, synergy.

Based on 1-km land surface model geophysical predictions within the United States Southern Great Plains (Red-Arkansas River basin), an observing system simulation experiment (OSSE) is carried out to assess the impact of land surface heterogeneity, instrument error, and parameter uncertainty on soil moisture products derived from the National Aeronautics and Space Administration Hydrosphere State (Hydros) mission. Simulated retrieved soil moisture products are created using three distinct retrieval algorithms based on the characteristics of passive microwave measurements expected from Hydros. The accuracy of retrieval products is evaluated through comparisons with benchmark soil moisture fields obtained from direct aggregation of the original simulated soil moisture fields. The analysis provides a quantitative description of how land surface heterogeneity, instrument error, and inversion parameter uncertainty impacts propagate through the measurement and retrieval process to degrade the accuracy of Hydros soil moisture products. Results demonstrate that the discrete set of error sources captured by the OSSE induce root mean squared errors of between 2.0% and 4.5% volumetric in soil moisture retrievals within the basin. Algorithm robustness is also evaluated for the case of artificially enhanced vegetation water content (W) values within the basin. For large W(> 3 kg x [m.sup.-2]), a distinct positive bias, attributable to the impact of sub-footprint-scale landcover heterogeneity, is identified in soil moisture retrievals. Prospects for the removal of this bias via a correction strategy for inland water and/or the implementation of an alternative aggregation strategy for surface vegetation and roughness parameters are discussed. Index Terms--Microwave remote sensing, observing system simulation experiment, soil moisture, spaceborne radiometry.

Radio-frequency interference (RFI) is an increasingly serious problem for passive and active microwave sensing of the Earth. To satisfy their measurement objectives, many spaceborne passive sensors must operate in unprotected bands, and future sensors may also need to operate in unprotected bands. Data from these sensors are likely to be increasingly contaminated by RFI as the spectrum becomes more crowded. In a previous paper we reported on a preliminary investigation of RFI observed over the United States in the 6.9-GHz channels of the Advanced Microwave Scanning Radiometer (AMSR-E) on the Earth Observing System Aqua satellite. Here, we extend the analysis to an investigation of RFI in the 6.9- and 10.7-GHz AMSR-E channels over the global land domain and for a one-year observation period. The spatial and temporal characteristics of the RFI are examined by the use of spectral indices. The observed RFI at 6.9 GHz is most densely concentrated in the United States, Japan, and the Middle East, and is sparser in Europe, while at 10.7 GHz the RFI is concentrated mostly in England, Italy, and Japan. Classification of RFI using means and standard deviations of the spectral indices is effective in identifying strong RFI. In many cases, however, it is difficult, using these indices, to distinguish weak RFI from natural geophysical variability. Geophysical retrievals using RFI-filtered data may therefore contain residual errors due to weak RFI. More robust radiometer designs and continued efforts to protect spectrum allocations will be needed in future to ensure the viability of spaceborne passive microwave sensing. Index Terms--Advanced Microwave Scanning Radiometer (AMSR), microwave radiometry, microwave remote sensing, radio-frequency interference (RFI).

Recent developments in reconstruction and resolution enhancement for microwave instruments suggest a possible tradeoff between computation, resolution, and downlink data rate based on postcollection reconstruction/resolution enhancement processing. The Hydrospheric State mission is designed to measure global soil moisture and freeze/thaw state in support of weather and climate prediction, water, energy, and carbon cycle studies, and natural hazards monitoring. It will use an active and passive L-band microwave system that optimizes measurement accuracy, spatial resolution, and coverage. The active channels use synthetic aperture radar-type processing to achieve fine spatial resolution, requiring a relatively high downlink data rate and ground processor complexity. To support real-time applications and processing, an optional postcollection reconstruction and resolution enhancement method is investigated. With this option, much lower rate real-aperture radar data are used along with ground-based postprocessing algorithms to enhance the resolution of the observations to achieve the desired 10-km resolution. Several approaches are investigated in this paper. It is determined that a reconstruction/resolution enhancement technique combining both forward- and aft-looking measurements enables estimation of 10-km resolution or better backscatter values at acceptable accuracy. Key tradeoffs to achieve this goal are considered. Index Terms--Hydrospheric State (HYDROS), reconstruction, resolution enhancement.

A spectral difference method is used to quantify the magnitude and extent of radio-frequency interference (RFI) observed over the United States in the Aqua AMSR-E radiometer channels. A survey using data from the AMSR-E instrument launched in May 2002 shows the interference to be widespread in the C-band (6.9 GHz) channels. The RFI is located mostly, but not always, near large highly populated urban areas. The locations of interference are persistent in time, but the magnitudes show temporal and directional variability. Strong and moderate RFI can be identified relatively easily using an RFI index derived from the spectral difference between the 6.9- and 10.7-GHz channels. Weak RFI is difficult to distinguish, however, from natural geophysical variability. These findings have implications for future microwave sensing at C-band, particularly over land areas. An innovative concept for radiometer system design is also discussed as a possible mitigation approach. Index Terms--Advanced Microwave Scanning Radiometer (AMSR), microwave radiometry, radio-frequency interference (RFI), land remote sensing.

In the present study, remote sensing of soil moisture is carried out using the Passive and Active L- and S-band airborne sensor (PALS). The data in this paper were taken from five days of overflights near Chickasha, OK during the 1999 Southern Great Plains (SGP99) experiment. Presently, we analyze the collected data to understand the relationships between the observed signals (radiometer brightness temperature and radar backscatter) and surface parameters (surface soil moisture, temperature, vegetation water content, and roughness). In addition, a radiative transfer model and two radar backscatter models are used to simulate the PALS observations. An integration of observations, regression retrievals, and forward modeling is used to derive the best estimates of soil moisture under varying surface conditions. Index Terms--Microwave, radar, radiometer, remote sensing, soil moisture.

The Advanced Microwave Scanning Radiometer (AMSR-E) on the Earth Observing System (EOS) Aqua satellite was launched on May 4, 2002. The AMSR-E instrument provides a potentially improved soil moisture sensing capability over previous spaceborne radiometers such as the Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager due to its combination of low frequency and higher spatial resolution (approximately 60 km at 6.9 GHz). The AMSR-E soil moisture retrieval approach and its implementation are described in this paper. A postlaunch validation program is in progress that will provide evaluations of the retrieved soil moisture and enable improved hydrologic applications of the data. Key aspects of the validation program include assessments of the effects on retrieved soil moisture of variability in vegetation water content, surface temperature, and spatial heterogeneity. Examples of AMSR-E brightness temperature observations over land are shown from the first few months of instrument operation, indicating general features of global vegetation and soil moisture variability. The AMSR-E sensor calibration and extent of radio frequency interference are currently being assessed, to be followed by quantitative assessments of the soil moisture retrievals. The AMSR-E instrument was developed by the National Space Development Agency of Japan (NASDA) and provided to the U.S. National Aeronautics and Space Administration. A similar instrument was launched in December 2002 on NASDA's ADEOS-II satellite. Index Terms--Hydrology, microwave, radiometry, remote sensing, satellite, soil moisture.

Data were acquired by the Passive and Active Land S-band airborne sensor (PALS) during the 1999 Southern Great Plains (SGP99) experiment in Oklahoma to study remote sensing of soil moisture in vegetated terrain using low-frequency microwave radiometer and radar measurements. The PALS instrument measures radiometric brightness temperature and radar backscatter at L- and S-band frequencies with multiple polarizations and approximately equal spatial resolutions. The data acquired during SGP99 provide (33) Many delegates opposed Article 23(3) of the ILC Draft on various grounds, including the possibility that the Council may disrupt the ICC's ability to function independently. (34) The ICC may be deprived of its jurisdiction in a particular situation if the situation remains under the Council's consideration for an indefinite period of time. (35) One veto by a permanent Council member can sufficiently thwart or block the ICC from action, which makes the ICC vulnerable to the Council's political motivations. (36) The search for a compromise between the ICC and the Council's powers coalesced around the 'Singapore Compromise.' (37) During PrepCom's August 1997 session, Singapore formally proposed an amendment revising the relationship structure between the ICC and the Council. (38) Singapore's proposal became the basis for the second option in Article 23(3) in the ILC Draft. (39) Singapore's proposal states, '[n]o investigation or prosecution may be commenced or proceeded with under this Statute where the Security Council has acting under Chapter VII of the Charter of the United Nations, given a direction to that effect.' (40) The Singapore Compromise proposes the opposite of what was required by Article 23(3) of the ILC Draft. (41) Thus, ICC proceedings may continue unless the Council formally decides to stop the process. (42) Since the adoption of a Security Council decision requires a minimum of nine affirmative votes in the Council, the ICC's proceedings may only be blocked by a 'concerted effort' of the Council members. (43) Theoretically, an ICC proceeding cannot be impeded even if all five permanent Council members joined to block the proceeding; nine positive votes are required to inhibit the block, including those from the five permanent members. (44) Based on Singapore's proposal, a 'negative veto' by the ILC text would be replaced by a positive vote. (45) Consequently, the ICC can exercise its jurisdiction unless it is directed not to do so by the Council. (46) In addition to the terms of the Singapore proposal, Canada recommended a 12-month renewable deferral period. (47) Costa Rica also suggested that deferral requests be made by a 'formal and specific decision' by the Security Council. (48) Furthermore, Singapore's proposal became the groundwork for Article 16 of the ICC Statute. The United Kingdom was the first permanent Security Council member to advocate changes in the relationship between the ICC and the Security Council. (49) A British draft for Article 10(2) (50) submitted during the March-April session of PrepCom in 1998 became the basis for the final draft of Article 16. (51) B. Legal Consequences Under Article 16, the Council may request that the ICC not investigate or proceed with a prosecution when the requisite majority of its members conclude that judicial action, or the threat of it, might harm the Council's efforts to maintain international peace and security pursuant to the U.N. Charter. (52) The ICC Statute does not define what it considers an 'investigation and prosecution.' (53) The statute indicates, however, that an 'investigation' involves an action that may be taken with respect to both a situation or an individual, while a 'prosecution' involves actions taken with respect only to a specific person. (54) The ICC prosecutor may initiate investigations upon receiving a referral about a particular situation by a State Party to the ICC Statute or the Security Council. (55) Upon commencement, an investigation must comprise the totality of investigative actions undertaken by the prosecutor under the ICC Statute in order to confirm the charges against a suspected individual or group. (56) After evaluating the available information, the ICC prosecutor can initiate an investigation if there is a reasonable basis to proceed. (57) Accordingly, one could conclude that still there are steps prior to the authorization of an investigation that the prosecutor is not precluded from taking, despite the fact that a Security Council's deferral under Article 16 took place. The Statute clearly permits the prosecutor to do the following: (1) conduct a preliminary examination as described in Article 15; (2) evaluate the information made available; (58) (3) seek 'information from States, organs of the United Nations, intergovernmental or non-governmental organizations, or other reliable sources that he or she deems appropriate;' and (4) receive 'written or oral testimony at the seat of the Court.' (59) The language of Article 16 is unclear, which makes interpreting the law problematic and difficult. Article 16 provides that '[n]o investigation or prosecution may be commenced or proceeded' after the Security Council issues a request. (60) Hence, that provision begs the question: 'When does an investigation or prosecution `commence?'' The commencement of an investigation may not necessarily depend on how the ICC's jurisdiction is triggered. The investigation commences when the ICC prosecutor determines that there is a 'reasonable basis to proceed' and renders a decision to that effect. (61) This is obviously a further or subsequent step to the preliminary examination and is probably based upon the decision of the Pre-Trial Chamber if the prosecutor is acting proprio motu. (62) Article 16 suggests that it may not only prevent the start of an investigation or prosecution, but it also may stop an investigation or a prosecution that is already underway. (63) Thus, one might wonder how problems arising from the Council's issuance of a deferral may be solved, especially once proceedings have begun. The deferral request raises a number of interesting questions. First, does a person arrested by a custodial state have to be set free? Second, what happens to a person who appeared before the ICC pursuant to a surrender request in accordance with Article 89(1)? Must that person stay in custody until the 12-month period lapses, or remain in custody as long as the Council decides? Third, what are the legal consequences of this decision with regard to that person's human rights? Fourth, what are the precautions required for the preservation of evidence? Neither the Statute nor the Rules of Procedure and Evidence appear to have definite answers to the above questions. From an analytical standpoint, however, one could draw a conclusion to the first question, beginning with an examination of the deferral decision. Although all states are bound by the Security Council's decisions, could the effects of that decision go beyond suspending the proceedings? In other words, a literal reading of Article 16 suggests that its power is limited by blocking the commencement of an investigation or prosecution, or stopping an on-going proceeding. (64) Hence, under a strict interpretation, a deferral decision does not mean that the defendant is no longer incriminated; rather, because the decision is procedural and based on political reasons, the proceedings are merely suspended for a specified period. A different interpretation would imply that the Council would be acting as a judicial body, which is obviously incorrect. The prosecutor can proceed with the investigation or prosecution once the deferral period has lapsed and the Council has not renewed the deferral. (65) Because releasing the person is not a legal consequence from that decision, it seems to be discretionary and not dependent on the decision. (66) A person should not be set free, however, when a case deals with the most heinous crimes. If a deferral continues for several years, then a person's right to 'be tried without undue delay' might be violated regardless of whether the person is under custody. (67) Although the prosecutor may conduct preliminary examinations after a deferral request is made, the prosecutor's efforts may be entirely futile or inadequate when destruction of evidence is imminent. (68) Absent the Security Council's guidance, the prosecutor may, under Article 54(3)(f), 'take necessary measures, or request the necessary measuresinformation on the sensitivities of multichannel low-frequency passive and active measurements to soil moisture for vegetation conditions including bare, pasture, and crop surface cover with field-averaged vegetation water contents mainly in the 0-2.5 kg [m.sup.-2] range. Precipitation occurring during the experiment provided an opportunity to observe wetting and drying surface conditions. Good correlations with soil moisture were observed in the radiometric channels. The 1.41-GHz horizontal-polarization channel showed the greatest sensitivity to soil moisture over the range of vegetation observed. For the fields sampled, a radiometric soil moisture retrieval accuracy of 2.3% volumetric was obtained. The radar channels showed significant correlation with soil moisture for some individual fields, with greatest sensitivity at 1.26-GHz vertical copolarized channel. However, variability in vegetation cover degraded the radar correlations for the combined field data. Images generated from data collected on a sequence of flight lines over the watershed region showed similar patterns of soil moisture change in the radiometer and radar responses. This indicates that under vegetated conditions for which soil moisture estimates may not be feasible using current radar algorithms, the radar measurements nevertheless show a response to soil moisture change, and they can provide useful information on the spatial and temporal variability of soil moisture. An illustration of the change detection approach is given. Index Terms--Microwave, radar, radiometer, remote sensing, soil moisture.

The Advanced Microwave Scanning Radiometer (AMSR) holds promise for retrieving soil moisture in regions with low levels of vegetation. Algorithms for this purpose have been proposed, but none have been rigorously evaluated due to a lack of datasets. Accordingly, the Southern Great Plains 1999 Experiment (SGP99) was designed to provide C-band datasets for AMSR algorithm development and validation. Ground observations of soil moisture and related variables were collected in conjunction with aircraft measurements using a C-band radiometer similar to the AMSR sensor (6.92 GHz), the Polarimetric Scanning Radiometer with its C-band scanhead (PSR/C). The study region has been the focus of several previous remote sensing field experiments and contains vegetation conditions compatible with the expected capabilities of C-band for soil moisture retrieval. Flights were conducted under a wide range of soil moisture conditions, thus providing a robust dataset for validation. A significant issue found in data processing was the removal of anthropogenic radio-frequency interference. Several approaches to estimating the parameters of a single-channel soil moisture retrieval algorithm were used. PSR/C soil moisture images show spatial and temporal patterns consistent with meteorological and soil conditions, and the dynamic range of the PSR/C observations indicates that the AMSR instrument can provide useful soil moisture information. Index Terms--Advanced microwave scanning radiometer (AMSR), passive microwave, soil moisture.

An algorithm is developed to solve the inverse problem for the retrieval of the soil moisture and temperature profiles based on remotely sensed observations of multispectral irradiance. A model of coherent wave radiative transfer and a model of coupled heat and moisture diffusion in porous media are combined in order to estimate the liquid volumetric water content and temperature profiles in a soil column using low-frequency passive microwave and infrared emitted radiation observations and without the use of empirical relations. The central purpose of this mainly theoretical paper is to pose the inverse problem and present the physics-based algorithm as the solution. The algorithm is here tested on a basic synthetic example in order to ascertain that the retrieval is feasible. Additional work in the future is necessary and planned in order to test the algorithm with field observations, extend it to include vegetation, and refine it for detail in the specification of heterogeneity in soil types and boundary conditions.

A special section is devoted to water as a subject of study in the natural sciences. Topics include karst, caves, hydrology and hydrogeology, and how water affects global and atmospheric processes.