Fact-checked by Grok 2 weeks ago

Scatterometer

A scatterometer is an active instrument designed to measure the backscattering of electromagnetic waves from the Earth's surface, primarily to determine near-surface speed and direction by analyzing how wind-generated waves modulate the return signal. These instruments operate in the Ku-band or C-band frequencies, transmitting pulses and receiving echoes from multiple incidence angles to resolve wind vectors with resolutions typically around 25 km. The development of scatterometers dates back to the early 1970s, with the first spaceborne instrument launched on NASA's mission in 1973, though it provided limited data due to the platform's short duration. A major milestone came in 1978 with the Scatterometer on the Seasat-A satellite, which delivered the first global measurements of ocean winds over 90% of the world's oceans for three months before mission failure, demonstrating the instrument's potential for weather and climate applications. Subsequent missions, such as the Active Microwave Instrument on ERS-1 (1991) and ERS-2 (1995), refined the technology using C-band frequencies for improved all-weather performance. Key missions in the 1990s and included NASA's NSCAT on Japan's ADEOS-I (1996–1997), which achieved high-accuracy wind retrievals over a 600 swath, and the SeaWinds instrument on QuikSCAT (1999–2009), providing near-daily global coverage that revolutionized tracking and El Niño monitoring. More recent operational scatterometers, like the Advanced Scatterometer (ASCAT) on the MetOp series—including -B (launched 2012) and MetOp-C (launched 2018), both ongoing as of 2025—and India's (launched 2017)—continue to support models with dual-polarization capabilities for enhanced ice and observations. NASA's ISS-RapidScat (2014–2018), repurposed from QuikSCAT hardware, uniquely sampled diurnal wind variations from the Station's orbit. As of November 2025, scatterometer data remain essential for marine safety, , and long-term climate studies, with ongoing missions like those on MetOp-B, MetOp-C, and ensuring continuous global wind monitoring.

Definition and Principles

Definition

A scatterometer is a scientific instrument designed to measure the backscattered portion of a transmitted beam of electromagnetic radiation from a medium such as the atmosphere, ocean surface, or material surfaces. While the term applies to both optical and radar systems, in Earth observation contexts, scatterometers typically refer to active microwave radar instruments that transmit pulses of energy and detect the returned signal to characterize scattering properties, distinguishing it from passive instruments that only receive natural emissions. The primary purpose of a scatterometer is to enable of surface characteristics, including roughness, over water, and coefficients of materials. Unlike spectrometers, which analyze the intensity of as a function of to identify , or radiometers, which passively measure emitted without transmission, scatterometers focus on the dynamics of backscattered energy to infer environmental or material properties. A in scatterometer measurements is the , denoted as \sigma^0, which quantifies the normalized or light per unit area and serves as the output for interpreting surface conditions. Scatterometers evolved from advancements in technologies during the mid-20th century, initially developed for applications.

Fundamental Principles

Scatterometers operate on the principle of elastic scattering, where incident electromagnetic radiation interacts with a surface or medium, resulting in redirection of the radiation without loss of energy, only a change in direction and phase. This process allows the instrument to probe surface roughness or particulate properties by analyzing the backscattered portion of the beam. In optical scatterometers, elastic scattering is governed by Rayleigh scattering for particles much smaller than the wavelength of light (typically d << λ, where d is particle diameter and λ is wavelength), which produces isotropic scattering with intensity proportional to 1/λ⁴, and Mie scattering for particles comparable in size to the wavelength (d ≈ λ), involving more complex angular patterns due to interference effects. In radar scatterometers, the primary mechanism is Bragg scattering, a resonant process where microwave signals backscattered from capillary-gravity waves on surfaces like the ocean constructively interfere when the wave crest spacing matches half the radar wavelength, enhancing the return signal from these short-wavelength surface features. The measurement process begins with the transmission of a directed beam of radiation toward the target, followed by collection of the backscattered signal using a receiver. The strength of this signal is used to compute the normalized backscattering coefficient, denoted σ⁰, which quantifies the radar reflectivity per unit area and is typically expressed in decibels (dB) as σ⁰ = 10 log₁₀(σ⁰_linear). For radar systems, σ⁰ is derived from the standard radar equation for distributed targets: σ⁰ = \frac{P_r (4\pi)^3 R^4}{P_t G^2 \lambda^2 A}, where P_r is received power, P_t is transmitted power, R is range, G is antenna gain, \lambda is wavelength, and A is the illuminated area (which is often proportional to R^2 for beam footprints, leading to an effective dependence of \sigma^0 \propto P_r R^2). The underlying relationship is captured by the bistatic radar equation for the received power from a point scatterer: P_r = \frac{P_t G_t G_r \lambda^2 \sigma}{(4\pi)^3 R^4}, where σ is the backscattering cross-section, G_t and G_r are transmit and receive gains, and R is the range (for monostatic systems, G_t = G_r = G and R_t = R_r = R). For distributed targets like extended surfaces, σ⁰ replaces σ normalized by the illuminated area, yielding P_r \propto \frac{P_t G^2 \lambda^2 \sigma^0}{(4\pi)^3 R^2}. In optical systems, an analogous bidirectional scatter-distribution function (BSDF) describes the scattered intensity as a function of incident and observation angles, computed similarly from measured irradiance ratios. Signal processing is essential to extract meaningful data from the raw returns. Received signals undergo and Doppler analysis to resolve and motion effects, with resolution achieved through multiple beam looks at varying angles to disambiguate directional information, such as wind vector orientation in applications. Calibration against known reference targets, like uniform trihedral corner reflectors or vicarious sites, ensures absolute values of σ⁰ or BSDF, correcting for system biases and atmospheric effects. Measurements are inherently limited by several factors. The backscattering coefficient σ⁰ (or BSDF) varies strongly with incidence angle, as steeper angles reduce the effective illuminated area and alter scattering geometry; (e.g., horizontal vs. vertical) influences the interaction with surface features, with often yielding weaker signals; and operating determines the scale of resolvable features, with higher frequencies probing finer roughness but suffering greater . Additionally, thermal noise from the receiver and multipath from surrounding structures can degrade , necessitating averaging over multiple pulses to mitigate speckle and fading effects.

Types

Optical Scatterometers

Optical scatterometers are instruments that utilize visible or near-infrared to measure scattering properties, typically employing sources such as lasers operating in the 650-900 nm range for illumination. These systems incorporate photodetectors or (CCD) arrays to capture diffuse reflections from the scattering medium, enabling precise quantification of scattered patterns. Designed for compactness and portability, they are often configured as table-top or handheld units suitable for ground-based deployments in controlled environments. In operation, optical scatterometers measure forward or within small sample volumes to assess phenomena, deriving key parameters such as the , which quantifies light attenuation due to and . The \beta is calculated using the formula \beta = -\frac{\ln(I / I_0)}{L}, where I represents the transmitted , I_0 the initial intensity, and L the path length through the medium. This approach is applied to determine densities in atmospheric samples or surface textures in materials, providing insights into distributions or roughness profiles without invasive sampling. Prominent examples include forward scatterometers deployed in runway visibility systems, which detect patches by monitoring diffusion from airborne to ensure safe operations. In industrial settings, these instruments evaluate and uniformity by analyzing scatter patterns to identify defects or inconsistencies in during processes. Optical scatterometers offer high for micro-scale analysis, achieving sub-micrometer precision in feature characterization, which is advantageous for detailed material inspections. However, their effective range is limited to tens of meters due to strong atmospheric and at visible wavelengths, restricting applications to near-field scenarios. Unlike radar-based systems, they are generally insensitive to target motion, focusing instead on static or low-velocity events. involves the use of reference targets, such as diffuse white standards made from materials like , which provide a known for normalizing measurements and ensuring accuracy across spectral bands.

Radar Scatterometers

Radar scatterometers are active microwave instruments designed for remote sensing of Earth's surface, particularly from spaceborne platforms, by transmitting pulses and measuring the backscattered signals to derive the normalized radar cross-section (NRCS, denoted as \sigma^0). These systems operate primarily in the C-band (approximately 5.3 GHz) or Ku-band (approximately 13.5 GHz), enabling penetration through clouds and all-weather imaging capabilities essential for global monitoring. The core architecture consists of a transmitter, , and , often employing fan-beam or pencil-beam configurations to achieve wide swath coverage. Fan-beam designs, as in the Advanced Scatterometer (ASCAT) on satellites, use multiple fixed antennas oriented at angles like 45° and 90° for fore, aft, and mid-swath views, providing a swath width of up to 550 km per side. Pencil-beam antennas, exemplified by the SeaWinds instrument on QuikSCAT, rotate conically to scan a broader swath of approximately 1800 km, utilizing real or synthetic techniques to resolve surface features. These components ensure continuous mapping as the satellite progresses in its orbit, with the modulated by according to the radar equation briefly referenced in fundamental principles. Operational modes involve pulsed transmission, typically with linear () for extended range resolution, though early concepts explored alternatives; scanning can be conical for rotating pencil-beams or fixed for fan-beam arrays, measuring \sigma^0 from ocean or land surfaces to characterize variations. Key features include polarimetric options such as vertical-vertical (), horizontal-horizontal (), and cross-polarizations ( or ), which aid in resolving ambiguities like by exploiting polarization-dependent . is generally 25-50 km, balancing coverage and accuracy for vector wind retrievals. Spaceborne implementations face power constraints, with peak transmit powers typically around 100–120 (orbital average power around 250 ) to manage energy budgets, and operate in () at altitudes around 800 km for optimal signal-to-noise ratios. Calibration relies on active transponders at ground sites for absolute accuracy and natural distributed targets like the , which provides stable \sigma^0 references with temporal stability better than 0.1 /year. These methods ensure radiometric precision within 0.5 , critical for quantitative geophysical inversions.

Applications

Meteorological and Oceanographic Applications

Scatterometers play a crucial role in meteorological and oceanographic applications by providing measurements of from the surface, which enable the retrieval of key environmental parameters. In vector retrieval, algorithms employing geophysical model functions (GMFs) such as CMOD5 for C-band instruments relate normalized cross-section (σ⁰) to near-surface and . These functions model the interaction between signals and capillary-gravity generated by s, allowing derivation of wind speeds ranging from 0.5 to 50 m/s with directional ambiguities resolved to approximately 180° through multiple azimuthal looks and ambiguity removal techniques. For instance, the QSCAT-12 GMF enhances accuracy for Ku-band data by incorporating refined hydrodynamic dependencies on wind relative to look . In hurricane and storm tracking, scatterometer-derived wind vectors supply essential for intensity estimation and path forecasting, particularly in data-sparse ocean regions. The QuikSCAT mission's SeaWinds instrument demonstrated this by delivering swath-based wind observations that improved advisories at the , enabling better assessment of maximum sustained winds and radial extent during events like in 2005. These measurements help forecasters refine storm size and timing for watch/warning issuance, reducing errors in intensity predictions by providing direct observations unaffected by cloud cover. Scatterometers also facilitate sea ice and wave analysis through distinct backscatter signatures. Sea ice edges are discriminated by σ⁰ differences, where open water exhibits higher variability and lower mean backscatter compared to ice-covered areas, allowing automated detection with accuracies exceeding 90% in polar regions using classifiers like on data from instruments such as CFOSAT's CSCAT. For ocean , anisotropic scattering patterns in σ⁰ reveal swell direction, as long-period swells produce azimuthally modulated backscatter due to aligned wave crests interacting with beams at varying incidence angles. This enables estimation of dominant swell propagation directions, aiding wave field modeling in operational forecasts. Integration of scatterometer data into models enhances atmospheric and oceanographic simulations via schemes at centers like ECMWF and NOAA. At ECMWF, assimilation of ERS and ASCAT winds reduces surface wind root-mean-square errors by up to 3.7% in coupled systems, improving global forecast skill through variational methods that incorporate σ⁰-derived vectors as observations. NOAA's similarly benefits from QuikSCAT inputs for initializing marine forecasts, though challenges like rain contamination—where attenuates signals and alters σ⁰, particularly in Ku-band—necessitate flags to mitigate biases in scenarios. A notable case study involves ERS-1 scatterometer data from the mid-1990s, which improved El Niño predictions by providing high-resolution wind fields over the equatorial Pacific during the 1997-1998 event buildup. These observations captured westerly wind bursts critical for triggering the warm phase, enabling coupled ocean-atmosphere models to better simulate anomalies and extend forecast lead times beyond traditional buoy networks.

Terrestrial and Environmental Applications

Scatterometer data have proven valuable for estimating content on land surfaces, leveraging the sensitivity of backscatter coefficient (σ⁰) to the soil's constant (ε), which varies with moisture levels. The Model (IEM) is commonly applied to model this relationship, where for rough surfaces, the IEM relates σ⁰ to ε, surface roughness, and incidence angle; this facilitates inversion algorithms to retrieve from C-band or Ku-band observations. For instance, the ERS Scatterometer has enabled large-scale mapping of in regions like western , achieving accuracies suitable for hydrological modeling when calibrated against ground measurements. In vegetation analysis, scatterometer measurements contribute to botanical studies by tracking phenological changes and dispersal patterns through temporal variations in . A seminal study utilized QuikSCAT scatterometer data to model connectivity, demonstrating that anemochorous (wind-dispersed) plant seeds can travel across continents, linking genetic diversity in to large-scale atmospheric transport. This approach highlighted how σ⁰ time series from Ku-band instruments correlate with canopy structure and , aiding in global assessments of ecological . For monitoring, scatterometers classify types by exploiting differences in responses between first-year and multi-year , often using ratios to distinguish surface properties like salinity and roughness. QuikSCAT data, for example, have been employed to separate seasonal (first-year) from perennial (multi-year) through enhanced at Ku-band frequencies, with ratios near 0 dB for mature types enabling automated mapping over the . Additionally, these ratios facilitate detection by contrasting high from rough targets against surrounding open water or thin . In and , time-series analysis of σ⁰ changes from instruments like the ERS and ASCAT scatterometers supports mapping by identifying anomalous drops due to water inundation and monitors crop health through correlations with vegetation water content and growth stages. Such applications have been integrated into assessments, where sustained low σ⁰ indicates drying, and into predictions by linking trends to harvest readiness. For global change studies, scatterometer-derived and vegetation indices track processes, as demonstrated in the where C-band data revealed temporal variability tied to ecosystem degradation and shifts. Emerging post-2016 applications incorporate scatterometer data into climate models for simulating thaw dynamics, using freeze/thaw state detection from C-band to parameterize carbon release and ground . ASCAT observations, for instance, have enhanced model validations by providing near-real-time indicators of thawing transitions in northern latitudes, improving predictions of from degrading soils.

Industrial and Scientific Applications

Scatterometers play a crucial role in semiconductor manufacturing through optical (OCD) , where scatterometry measures nanoscale features such as line widths ranging from 10 to 100 nm by analyzing patterns from periodic structures. This technique employs ellipsometric scattering models to infer s, profiles, and film thicknesses, enabling non-destructive inline process control in advanced nodes like gate-all-around transistors. For instance, scatterometry has been integrated with other tools like CD-SEM to provide comprehensive geometry data, including bottom widths, supporting high-precision fabrication. In precision manufacturing sectors such as and , lab-based scatterometers characterize with arithmetic average roughness () values below 1 μm, using angular resolved to profile defects and ensure component quality. Optical setups, often employing Czerny-Turner configurations with detectors, quantify diffuse from polished surfaces, distinguishing roughness-induced effects from material anomalies in applications like mirrors. These measurements support deterministic correction in computer-controlled optical surfacing, vital for high-performance . Beyond Earth-based industry, radar scatterometers have advanced non-terrestrial science, notably in NASA's Cassini mission (2004–2017), where the instrument's scatterometer mode mapped Titan's surface composition and identified vast dune fields composed of organic particles. By analyzing signatures, the data revealed dune equivalents to a global layer 0.6–6 m deep, informing models of Titan's geological and atmospheric interactions. This approach highlighted radar scatterometry's utility in probing extraterrestrial terrains shrouded in haze. In material science, scatterometers assess in composite materials, modeling optical from densely packed particles to evaluate structural and interaction properties. Similarly, in biomedical applications, coherent scatterometry measures coefficients, resolving orientations and substructures in samples without labels. These techniques provide quantitative insights into biological patterns, aiding in non-invasive diagnostics. Recent advancements since 2020 integrate with scatterometry for solving inverse modeling challenges, where algorithms reconstruct nanostructures from scattering data more efficiently than traditional methods. neural networks, for example, enhance Mueller-matrix scatterometry accuracy in metrology, reducing computational demands while improving parameter inference for complex features. This AI-driven approach has accelerated process monitoring in high-volume production.

History

Early Development

The conceptual foundations of scatterometers emerged in the through research focused on ocean backscatter, particularly at NASA's (JPL) and other institutions, where scientists established empirical links between returns from sea surfaces and near-surface wind speeds. These studies built on World War II-era observations of sea clutter, initially viewed as noise, but were advanced by experiments demonstrating that normalized radar cross-section (NRCS) variations correlated with wind-induced , serving as precursors to altimetry and wind vector retrieval techniques. Initial prototypes in the included ground-based optical scatterometers designed to measure atmospheric by quantifying forward light scattering from aerosols and , with early field tests validating their performance against traditional transmissometers. Concurrently, radar-based prototypes, such as NASA's improved pencil-beam scatterometers operating at frequencies like 13.3 GHz, conducted tests to characterize over oceans and land, providing foundational data on dependence on incidence angle and environmental factors. These efforts transitioned from analog systems to more reliable designs, enabled by advances in solid-state amplifiers that allowed compact, portable with enhanced power efficiency and reduced size compared to vacuum-tube predecessors. The first spaceborne demonstration occurred during the missions (1973–1974), where the S-193 instrument—a combined 13.9 GHz , , and —measured and , proving the feasibility of orbital despite the program's abbreviated duration due to spacecraft issues. Early techniques, emerging in the , facilitated onboard data handling and ground analysis of these returns, overcoming limitations in real-time computation. However, challenges included ambiguities in retrieval, as initial pencil-beam geometries provided speed estimates but required multiple looks for vector resolution, and in-orbit difficulties, addressed through reference targets like cells to correct for instrument drift and atmospheric effects.

Major Satellite Missions

The mission, launched by on June 27, 1978, featured the first spaceborne radar scatterometer, operating in the Ku-band to measure global ocean surface wind vectors with a swath width of approximately 1,000 km. The instrument provided continuous data for 105 days until a power system failure ended operations on October 10, 1978, yielding pioneering datasets on sea-surface winds, waves, and ice that demonstrated the feasibility of scatterometry for ocean monitoring. The European Remote-Sensing satellites ERS-1 and ERS-2, launched by the (ESA) on July 17, 1991, and April 21, 1995, respectively, carried the Active Microwave Instrument (AMI) with a C-band scatterometer mode for measuring winds and extent. ERS-1 operated until March 2000, while ERS-2 extended coverage until July 2011, providing overlapping observations that ensured continuity and supported long-term studies of wind patterns and polar ice dynamics. Japan's Advanced Earth Observing System (ADEOS-I), launched in August 1996, carried NASA's Ku-band Scatterometer (NSCAT), which provided high-accuracy ocean wind retrievals over a 600 km swath with 25-km resolution, covering more than 90% of ice-free oceans every two days. The instrument operated from September 1996 until the satellite's failure in June 1997 due to a power issue, delivering valuable global datasets that advanced and climate research. NASA's QuikSCAT mission, launched on June 19, 1999, incorporated the SeaWinds Ku-band scatterometer, which achieved near-global ocean coverage of over 90% with 25-km resolution wind vectors, filling a gap after the failure of NSCAT on ADEOS-I. Operational until November 2009, QuikSCAT data proved essential for tropical cyclone intensity forecasting and numerical weather prediction models. The Advanced Scatterometer (ASCAT), a C-band instrument on the EUMETSAT MetOp series, began operations with MetOp-A in 2006 and continues through MetOp-B (launched 2012) and MetOp-C (launched 2018), delivering 25-km and 12.5-km resolution wind products over 95% of the ice-free oceans. ASCAT's vertical and horizontal polarization measurements enhance wind retrieval accuracy in diverse conditions, maintaining a continuous record for operational meteorology. NASA's RapidScat, deployed on the in September 2014 using refurbished SeaWinds hardware, provided Ku-band observations at 25-km resolution from a non-Sun-synchronous , enabling diurnal cycle studies until its decommissioning in 2016. This short mission bridged gaps in ocean data post-QuikSCAT while validating instrument performance in a unique orbital environment. Launched in December 2016, NASA's (CYGNSS) consists of eight microsatellites employing GPS reflectometry—a bistatic technique—to measure ocean surface winds, particularly in the low-incidence angle regime inside tropical cyclones where traditional struggle. The constellation achieves frequent revisits over hurricane-prone regions, supporting improved storm forecasting and ongoing data collection as of 2025. Post-2020 developments include integration of scatterometer-derived winds with the NASA-CNES , launched in December 2022, where Ka-band complements wind data for enhanced and analyses. The legacy of these lies in their archived datasets, which span over four decades and enable long-term climate studies, such as trends in global wind patterns and ocean-atmosphere interactions, while ongoing series like MetOp-SG, with A1 launched in August 2025, ensure uninterrupted, high-resolution coverage as of 2025.

References

  1. [1]
    Scatterometry - Overview - fsu/coaps - Florida State University
    What is Scatterometry? Scatterometers are unique among satellite remote sensors in their ability to determine the wind direction over water.
  2. [2]
    [PDF] ISS - RapidScat - NASA Jet Propulsion Laboratory (JPL)
    Radar scatterometers are the only remote- sensing instruments that can provide accurate, frequent, high-resolution measurements of ocean-surface wind speed and ...
  3. [3]
    [PDF] SeaWinds ALGORITHM THEORETICAL BASIS DOCUMENT
    In particular, satellite-borne radar scatterometers are the only remote sensing systems presently ca- pable of providing accurate, frequent, high-resolution ...
  4. [4]
    Remote Sensing - NASA Earth Observatory
    Sep 17, 1999 · A scatterometer is a high frequency microwave radar designed specifically to measure backscattered radiation. Over ocean surfaces, measurements ...
  5. [5]
    Optical scatterometer | Engineering Interdisciplinary Capstone
    An optical scatterometer measures light scattering properties of a material by shining a laser and measuring scattered power as a function of angle.
  6. [6]
    NASA Scatterometer Climate Record Pathfinder (Center for Remote ...
    Scatterometers are active microwave sensors, i.e., they are radars that transmit a signal and measure the returned echo power. Radiometers are passive microwave ...<|control11|><|separator|>
  7. [7]
    Scatterometry | Learning Weather at Penn State Meteorology
    So, a scatterometer is an active remote sensor--it emits pulses of microwave radiation and measures the radiation that backscatters to the unit, similar to ...
  8. [8]
    [PDF] Active techniques for wind observations: scatterometer - ECMWF
    Sep 12, 2014 · The scatterometer is an active microwave instrument which is capable of measuring the normalized radar cross section (or backscatter σ0) of the ...
  9. [9]
    Metop-SG SCA L1B data guide | EUMETSAT - User Portal
    Scatterometers are all weather instruments, where the basic measurement taken is often called radar backscatter, Normalised Radar Cross Section (NRCS) or σ0.
  10. [10]
    QuikSCAT - Scatterometry - NASA Earth Observatory
    Jul 23, 1999 · The first scatterometer flew as part of the Skylab missions in 1973 and 1974, demonstrating that spaceborne scatterometers were indeed feasible.
  11. [11]
    Early days of microwave scatterometry: RADSCAT to SASS
    Professor Richard K. Moore is the father of microwave scatterometry and this paper discusses the history of the instrument development (with emphasis on the ...
  12. [12]
    The Physics of Scattering - Ocean Optics Web Book
    Oct 13, 2021 · Elastic scattering occurs when light travels from a region with one index of refraction into a region with a different index of refraction.Missing: scatterometer | Show results with:scatterometer
  13. [13]
    Radar scattering and equilibrium ranges in wind‐generated waves ...
    May 15, 1987 · A composite divided scale model for radar backscatter from the ocean surface is constructed. The primary scattering mechanism is assumed to be Bragg scattering.
  14. [14]
    [PDF] Radar Scatterometry--- An Active Remote Sensing Tool
    Here we describe the function of a scatterometer, and the principles of the basic system ... The fundamental FM principle is illustrated by Figure 24.
  15. [15]
    [PDF] Introduction to Scatterometry - NASA Winds
    May 29, 2024 · Winds over the ocean create small capillary-gravity waves (“cat's paws”) which roughen surface. - Roughness is related to wind speed and ...
  16. [16]
    Scatter and BSDF Measurements: Theory and Practice
    Light can be scattered or rescattered during its propagation to our eyes or to a detector by rough surfaces, textures, and particulates. This scattered light is ...
  17. [17]
    Petri-plate, bacteria, and laser optical scattering sensor - Frontiers
    An optical scattering sensor designated BARDOT (bacterial rapid detection using optical scattering technology) that uses a red-diode laser.<|separator|>
  18. [18]
    Optical Measurement Systems for Industrial Inspection XI - SPIE
    Aug 22, 2019 · In our contribution we will present a self-built scatterometer that is based on a Czerny-Turner geometry in conjunction with a CMOS-camera ...
  19. [19]
    Imaging Scatterometer for Observing Changes to Optical Coatings ...
    Our instrument uses an industrial oven with viewports to observe coating scatter and damage during annealing. ... Uniform, Dropshadow. Font Family.Missing: uniformity | Show results with:uniformity
  20. [20]
    Extinction coefficients from aerosol measurements - ScienceDirect
    In this contribution, we develop a model that describes light extinction in the presence of arbitrary aerosols.
  21. [21]
    An Aerosol Extinction Coefficient Retrieval Method and ...
    This study proposes simple methods to solve this problem, which yield reasonable extinction coefficients at the three effective RGB wavelengths.
  22. [22]
    [PDF] United States Experience Using Forward Scattermeters for Runway ...
    Although fog is the most common obstruction to vision reducing the visibility into the RVR region, other obstructions to vision, such as snow, smoke, dust ...
  23. [23]
    [PDF] Bidirectional Reflectance Measurements of Low-Reflectivity Optical ...
    Dec 6, 2018 · The method of application of Z302 was the next consideration because it plays a vital role in the uniformity of the coating. Applying a coating ...
  24. [24]
    Perspective: Optical measurement of feature dimensions and ...
    May 14, 2018 · The term scatterometry refers to the use of optical scattering from a period array to determine feature dimensions and shape. Here we discuss ...
  25. [25]
    Atmospheric absorption and scattering impact on optical satellite ...
    Oct 7, 2021 · Further advantages of optical FSO—besides spectrum availability—is its increased power efficiency, higher data rates, avoidance of ...
  26. [26]
    Calibrating with a White Reference for a Baseline | Malvern Panalytical
    Feb 26, 2020 · Spectralon is uniquely suited as a white reference material because of its property of Lambertian reflectance. It reflects light at all angles equally creating ...Missing: targets | Show results with:targets
  27. [27]
    Diffuse Reflectance Standard Calibrations | Request Service
    As critical components for instrument calibration, we recommend these optical reference materials of 8/H spectral reflectance factor should be periodically ...Missing: scatterometer white
  28. [28]
    QuikScat / SeaWinds - Remote Sensing Systems
    The SeaWinds instruments are the third in a series of NASA scatterometers that operate at Ku-band (i.e., a frequency near 14 GHz). The first Ku-Band ...Missing: exact | Show results with:exact
  29. [29]
    CFOSAT Rotating Fan‐Beam Scatterometer Backscatter ...
    Nov 5, 2021 · The CMFU and CTRU are Ku-band radar electronics units, and include an RF transmitter, a receiver, and waveguide switches. All active electronics ...Missing: components | Show results with:components
  30. [30]
    Validation of Backscatter Measurements from the Advanced ...
    The Advanced Scatterometer (ASCAT) on the Meteorological Operational (MetOp) series of satellites is designed to provide data for the retrieval of ocean wind ...
  31. [31]
    QuikSCAT - eoPortal
    Measurement technique: The SeaWinds instrument transmits microwave pulses to the ocean surface and measures the backscattered power received. The sea surface ...
  32. [32]
    Higher-order calibration on WindRAD (Wind Radar) scatterometer ...
    Oct 20, 2023 · WindRAD (Wind Radar) is a dual-frequency rotating fan-beam scatterometer instrument on the FY-3E (FengYun-3E) satellite.
  33. [33]
    [PDF] ASCAT – Metop's Advanced Scatterometer
    The need to provide adequate radiometric resolution is a factor in the dimensioning of antenna gain, transmitter power and receiver noise figure. A second.
  34. [34]
    [PDF] calibration and validation of the advanced scatterometer on metop-b
    We examine ASCAT-A and B data over the Amazon rainforest in the region enclosed by longitudes [-. 70° to -60.5°] E and latitudes [-5° to 2.5°] N, during ...
  35. [35]
    An improved C‐band scatterometer ocean geophysical model ...
    Mar 6, 2007 · In this paper CMOD5, a new C-band geophysical model function (GMF), is derived on the basis of measurements from the scatterometer on board ...
  36. [36]
    Oceansat-2 Scatterometer Level 2B Ocean Wind Vectors in 12.5km ...
    ... wind vector cell. This newest version contains an improved geophysical model function (GMF), known as QSCAT12, consistent with the Remote Sensing Systems ...
  37. [37]
    A Scatterometer Geophysical Model Function for Climate-Quality ...
    Oct 1, 2015 · We started with the European scatterometer ASCAT (Figa-Saldaña et al. 2002; Verspeek et al. 2010) on Metop-A and developed a new C-band GMF ...
  38. [38]
    [PDF] The Operational Use of QuikSCAT Ocean Surface Vector Winds at ...
    Accurate wind radii analyses and forecasts are a critical factor in determining the size and timing of tropical storm and hurricane watch and warning areas, and ...
  39. [39]
    [PDF] operational evaluation of quikscat ocean surface vector winds in
    The average biases of the. QuikSCAT maximum wind speeds were then calculated for tropical depressions, tropical storms, and hurricanes binned by category on the ...
  40. [40]
    Sea Ice Monitoring with CFOSAT Scatterometer Measurements ...
    This research verifies the capability of CSCAT in monitoring polar sea ice using a machine learning-aided random forest classifier.
  41. [41]
    [PDF] Algorithm Theoretical Basis Document for the Global sea-ice edge ...
    Feb 5, 2021 · The use of scatterometer data in the OSI SAF sea-ice analysis started with the C-band radar scatterometers on-board the research satellites ERS- ...
  42. [42]
    Measurement of microwave backscattering signatures of the ocean ...
    Nov 15, 1986 · The azimuth anisotropic signatures for Ka band are confirmed to be similar to those for X band, and the wind speed dependences are analyzed for ...
  43. [43]
    Impact of Scatterometer Surface Wind Data in the ECMWF Coupled ...
    The assimilation of scatterometer data has reduced the background surface wind root-mean-square error in the coupled and uncoupled assimilation systems by 3.7% ...Missing: contamination | Show results with:contamination
  44. [44]
    [PDF] Impact of ERS Scatterometer Winds in ECMWF's Assimilation System
    ... scatterometer data. It has been shown that the ERS scatterometer data is of high consistent quality without cloud/rain contamination problems. ERA-40.
  45. [45]
    [PDF] REMOTELY SENSED WINDS AND WIND STRESSES FOR MARINE ...
    The main weaknesses of scatterometers are rain contamination for some rain conditions (far more so for Ku-band than C-band), a lack of data near land (15km for ...<|control11|><|separator|>
  46. [46]
    Evolution of 1996–1999 La Niña and El Niño conditions off the ...
    Dec 31, 2002 · From 1996 to present, scatterometers on the European Remote Sensing satellites (ERS-1 and ERS-2) made measurements of wind speed and direction.3. Results · 3.5. 2. El Niño (may 1997... · 4. Discussion
  47. [47]
    Evaluation of the Oh, Dubois and IEM Backscatter Models Using a ...
    Jan 11, 2017 · The aim of this paper is to evaluate the most used radar backscattering models (Integral Equation Model “IEM”, Oh, Dubois, and Advanced Integral Equation Model ...
  48. [48]
    Large-Scale Soil Moisture Mapping in Western Africa using the ERS ...
    Mar 23, 2025 · The observation of the whole continental surfaces with active microwave data has recently started with the launch of C-band wind scatterometers ...
  49. [49]
    [PDF] Evaluation of QuikSCAT data for Monitoring Vegetation Phenology
    The analysis indicates that QuikSCAT signal appears to be an accurate tool for monitoring vegetation phenology. Page 8. 4. 1 Introduction. Vegetation phenology ...
  50. [50]
    [PDF] Multi-year Arctic Sea Ice Classification Using QuikSCAT
    This thesis uses microwave scatterometer data from. QuikSCAT and radiometer data to analyze intra- and interannual trends in first-year and multi-year Arctic ...<|separator|>
  51. [51]
    Polar Sea Ice Monitoring Using HY-2B Satellite Scatterometer and ...
    Remund and Long [11,12] first used the polarization ratio and backscattering coefficient to distinguish sea ice from open sea water automatically based on Ku ...
  52. [52]
    Endeavours of Scatterometer Satellite (SCATSAT-1) in earth ...
    As compared to the optical dataset, scatterometers are found to be more suitable in the estimation of soil erosion, droughts, and harvesting crops. SCATSAT-1 ...
  53. [53]
    [PDF] analysis of time-series backscatter of ers-2 c-band scatterometer ...
    The study indicated the potential of C-band scatterometer data for monitoring temporal variability for modelling and monitoring desert ecosystem.
  54. [54]
    Dependence of C-Band Backscatter on Ground Temperature, Air ...
    Jan 19, 2018 · Microwave remote sensing has found numerous applications in areas affected by permafrost and seasonally frozen ground.
  55. [55]
    Evaluation and Enhancement of Permafrost Modeling With the ...
    Nov 8, 2017 · Permafrost dynamics play a vital role in the water, energy, and carbon cycles. Climate variability predominately controls the general patterns ...
  56. [56]
    Dimensional Metrology for Nanoscale Patterns | NIST
    Dimensional metrology and control is a critical component of semiconductor fabrication. ... scatterometry, Critical Dimension Atomic Force Microscopy (CD ...
  57. [57]
    Scatterometry Critical Dimension Solution for Gate All Around Sheet ...
    In this paper, a scatterometry critical dimension (SCD) solution for the GAA sheet-specific measurement from various GAA structures is presented.
  58. [58]
    Combination of Mass Metrology with Scatterometry to obtain bottom ...
    CD-SEM gives the top critical dimension (CD) of trenches and scatterometry provides the trench depth. An average value for the trench bottom width or bottom ...
  59. [59]
    [PDF] nistir 7426 - NIST Technical Series Publications
    also used to characterize scattering from steel surfaces, demonstrating capability to distinguish between scattering from surface roughness and material ...
  60. [60]
    Astronomical Optics: Design, Manufacture, and Test of Space ... - SPIE
    Computer-Controlled Optical Surfacing (CCOS) is a key technique for high-precision optics, enabling deterministic correction of surface errors in applications ...
  61. [61]
    [PDF] Cassini RADAR Users Guide - PDS Imaging Node
    The surface of Saturn's moon Titan, shrouded in haze, has been revealed by data returned from the Cassini Orbiter, as well as from descent and surface images ...
  62. [62]
    [PDF] Transient climate effects of large impacts on Titan - CORE
    May 20, 2013 · Le Gall et al. (2011) find that Titan's sand dunes to- day correspond to the equivalent of a global layer 0.6-6 m deep. At current rates, this ...
  63. [63]
    Cassini's radar observes Titan's tropical dune fields
    Jan 23, 2012 · While Titan's dunes resemble in many ways the features found on Earth, they are made of tiny particles of organic (carbon-rich) material which ...Missing: composition | Show results with:composition
  64. [64]
    Modeling scatter in composite media - SPIE Digital Library
    Aug 29, 2008 · A theoretical model of optical scattering in materials consisting of densely packed spherical particles is developed that can be used to ...Missing: diffuse | Show results with:diffuse
  65. [65]
    Coherent Fourier scatterometry reveals nerve fiber crossings in the ...
    Here, we present a method that measures these scattering patterns in monkey and human brain tissue using coherent Fourier scatterometry with normally incident ...
  66. [66]
    Scattered Light Imaging: Resolving the substructure of nerve fiber ...
    Scatterometry allows to measure the full scattering pattern, but only for brain regions ≥ 100 µm (Menzel and Pereira, 2020a). In Scattered Light Imaging (SLI), ...
  67. [67]
    Machine learning aided solution to the inverse problem in optical ...
    Mar 15, 2022 · In this paper, we propose a machine-learning-enabled reconstruction method (MLER) for solving to the inverse problem in optical scatterometry.
  68. [68]
    Efficient deep-learning ResNet architectures for Mueller-matrix ...
    Aug 8, 2025 · As an indirect measurement technique, scatterometry inherently solves an inverse problem, where desired parameters are inferred from captured ...
  69. [69]
    2023 IRDS Metrology
    Scatterometry models typically assume uniform optical properties of line and background materials, although surface ... reflectance measurements on materials ...
  70. [70]
    Challenges to Satellite Sensors of Ocean Winds - AMS Journals
    The scientific and empirical basis for using microwave radar to infer sea surface winds was established in the. 1960s. Empirical observations in wave tanks and ...<|control11|><|separator|>
  71. [71]
    [PDF] ISS–RapidScat Launch - NASA Jet Propulsion Laboratory (JPL)
    Sep 20, 2014 · In the 1960s, scientists established a link between the waves causing backscatter and the speed of wind at the ocean's surface. They also ...<|control11|><|separator|>
  72. [72]
    Field Test of a Forward Scatter Visibility Meter. - DTIC
    Field tests of a forward scatter visibility instrument were carried out in August 1970 at Cutler, Maine. The performance characteristics of the new ...
  73. [73]
    [PDF] Science Opportunities Using the NASA Scatterometer on N-ROSS
    Feb 1, 1985 · A more complete review of the historical development of scatterometer systems to measure surface winds over the ocean can be found in Moore and ...
  74. [74]
    [PDF] A SYSTEM ANALYSIS OF THE 13.3 GHz SCATTEROMETER
    This document is primarily concerned with the performance of the 13.3 GHz airborne scatterometer system which is used as one of several Johnson Space Center ( ...Missing: advances | Show results with:advances
  75. [75]
    Skylab Space Station - eoPortal
    Jun 15, 2012 · Nonetheless, the S-193 experiment demonstrated that centimetric backscatter from the ocean could be detected by spaceborne instruments at ...
  76. [76]
    [PDF] skylab s-193 radscat microwave measurements of sea surface winds
    The S~193 Radscat was a combined 13.9 GHz radiometer/scatterometer which operated aboard Sky- lab. The antenna beam was approximately circular with a two-way ...
  77. [77]
    Seasat - Earth Missions - NASA Jet Propulsion Laboratory
    Seasat operated in Earth orbit for 105 days, measuring sea-surface winds and temperatures, wave heights, atmospheric liquid water content, sea ice features and ...Missing: details | Show results with:details
  78. [78]
    Seasat | NASA Earthdata
    Seasat was in continuous operation for 106 days and served as the precursor to many of NASA's later missions including Nimbus-7, TOPEX/Poseidon, NSCAT, QuikSCAT ...Missing: details | Show results with:details
  79. [79]
    ERS - ESA Earth Online
    The ERS programme was composed of two missions, ERS-1 and ERS-2, which together observed the Earth for 20 years, from 1991 to 2011.
  80. [80]
    ERS-1 (European Remote-Sensing Satellite-1) - eoPortal
    Feb 29, 2024 · The ERS-1 was the first environmental monitoring satellite developed by ESA. The mission detected land and ocean surface change and provided observation data.Spacecraft · Launch · Mission Status
  81. [81]
    QuikSCAT Mission | PO.DAAC / JPL / NASA
    The SeaWinds scatterometer on QuikSCAT began producing science quality data on 19 July 1999. Since launch, the SeaWinds instrument provided.
  82. [82]
    OSI SAF Metop-A ASCAT L2 winds Data Record - KNMI scatterometer
    EUMETSAT has reprocessed the Metop-A ASCAT level 1b data record up to March 2014 using uniform calibration settings and one single processing software ...
  83. [83]
    ISS-RapidScat | NASA Jet Propulsion Laboratory (JPL)
    NASA's International Space Station Rapid Scatterometer (ISS-RapidScat) Earth science instrument has ended operations following a successful two-year mission ...
  84. [84]
    ISS-Rapid Scatterometer - NASA's Earth Observing System
    Scatterometers are radar instruments that can measure near-surface wind speed and direction over the ocean, and have proved to be extremely valuable for weather ...
  85. [85]
    CYGNSS | PO.DAAC / JPL / NASA
    The Cyclone Global Navigation Satellite System (CYGNSS), launched on 15 December 2016, is a NASA Earth System Science Pathfinder Mission that is intended to ...
  86. [86]
    Teaching Old Data New Tricks | NASA Earthdata
    Jul 28, 2020 · Scatterometer data have proven useful in global climate studies largely due to the length of the data record. The data cover more than 20 years ...
  87. [87]
    NASA Scatterometer Climate Record Pathfinder (Center for Remote ...
    The NASA Scatterometer Climate Record Pathfinder (SCP) is a NASA sponsored project to develop scatterometer-based data time series to support climate studies.Missing: legacy | Show results with:legacy