The HYDROS mission: requirements and system design

Njoku, E.; Spencer, M.; McDonald, K. C.; Smith, J. G.; Houser, Paul R.; Doiron, T.; O'Neill, P.; Girard, Ralph; Entekhabi, Dara

doi:10.1109/aero.2004.1367701

Cited by 5 publications

(6 citation statements)

References 9 publications

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“…Discussion of TABLE I HYDROS INSTRUMENT CHARACTERISTICS the instrument measurement errors and sampling characteristics is deferred to Section VI. Details of the Hydros mission and instrument design are provided in [9] and [10].…”

Section: Hydros Instrument Designmentioning

confidence: 99%

“…where is a correction parameter for the combined effect of the surface roughness and vegetation and defined as (10) is a vegetation correction factor defined as (11) and the total emissivity is…”

Section: Multipolarization Regression Algorithmmentioning

confidence: 99%

“…Hydros is designed to provide global maps of the earth's soil moisture and freeze/thaw state every 2-3 days for weather and climate prediction, water, energy, and carbon cycle studies, and natural hazards monitoring. Hydros utilizes a unique active and passive L-band (1.2-1.4 GHz) microwave concept to simultaneously measure microwave emission and backscatter from the surface across a wide spatial swath [9], [10]. The Hydros antenna is an approximately 6-m diameter deployable lightweight mesh reflector that provides footprint sizes of approximately 40 km for the radiometer and 30 km for the radar.…”

Section: Introductionmentioning

confidence: 99%

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An observing system simulation experiment for hydros radiometer-only soil moisture products

Crow

Chan

Entekhabi

et al. 2005

IEEE Trans. Geosci. Remote Sensing

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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 () values within the basin. For large (3 kg m 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.

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Section: Hydros Instrument Designmentioning

confidence: 99%

Section: Multipolarization Regression Algorithmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An observing system simulation experiment for hydros radiometer-only soil moisture products

Crow

Chan

Entekhabi

et al. 2005

IEEE Trans. Geosci. Remote Sensing

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“…The antenna is an approximately 6-m diameter deployable mesh reflector that provides 3-dB footprint sizes of approximately 40 km for the radiometer (dictated by the one-way gain pattern) and 28 km for the radar (dictated by the two-way gain pattern). The "single-look" radar resolution is enhanced to as fine as 300-700 m by using unfocused SAR processing that uses both range and Doppler processing [18]. From this, a multilook, calibrated output product is generated at 3-km resolution.…”

Section: Hydros Design Summarymentioning

confidence: 99%

“…Such compensation can be accomplished by using collocated scatterometer observations [16], [17]. The Hydrospheric State (HYDROS) mission was designed to obtain combined radiometer/scatterometer soil moisture retrievals [14], [18], [19]. To improve the spatial resolution of HYDROS soil moisture measurements, unfocused SAR processing is employed for processing HYDROS scatterometer measurements.…”

Section: Introductionmentioning

confidence: 99%

Spatial resolution and processing tradeoffs for HYDROS: application of reconstruction and resolution enhancement techniques

Long

Spencer

Njoku

2005

IEEE Trans. Geosci. Remote Sensing

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Abstract-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.

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