Calibration error of L‐band sky‐looking ground‐based radiometers

Delahaye, Jean-Yves; Golé, P.; Waldteufel, Philippe

doi:10.1029/2001rs002490

Cited by 24 publications

(17 citation statements)

References 4 publications

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“…The biases are lower than 0.3 K. For black body targets, only one point gives errors higher than 3 K. This single occurrence is likely associated with an error in recording the black body physical temperature during the stabilitycheck. The higher error in the sky measurements could be related to the fact that the sky emission might vary slightly depending upon the observed portion of the sky due to the variability in sky background temperatures measured when the antenna beamwidth crosses the galactic plane (increases by 1-3 K) and due to potential contributions from the sun and moon (Delahaye et al, 2002;Le Vine et al, 2005). Further analysis of these effects will be evaluated in future campaigns.…”

Section: Radiometer Calibration Results and Instrument Stability Evalmentioning

confidence: 99%

“…A three-point calibration procedure using the sky, ambient, and heated warm targets was developed to account for the radiometer's calibration nonlinearity and improve the accuracy over the full range of measured T B . The reference sky T B at L-band was considered to be ≈ 5 K for both polarizations based on previously published data from both measured and modelled sources (Pellarin et al, 2016;Lemmetyinen et al, 2016;Le Vine et al, 2005;Delahaye et al, 2002).…”

Section: Calibration Measurement Procedure/post-processingmentioning

confidence: 99%

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Radio-frequency interference mitigating hyperspectral L-band radiometer

Toose

Roy

Solheim³

et al. 2017

Geosci. Instrum. Method. Data Syst.

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Abstract. Radio-frequency interference (RFI) can significantly contaminate the measured radiometric signal of current spaceborne L-band passive microwave radiometers. These spaceborne radiometers operate within the protected passive remote sensing and radio-astronomy frequency allocation of 1400-1427 MHz but nonetheless are still subjected to frequent RFI intrusions. We present a unique surfacebased and airborne hyperspectral 385 channel, dual polarization, L-band Fourier transform, RFI-detecting radiometer designed with a frequency range from 1400 through ≈ 1550 MHz. The extended frequency range was intended to increase the likelihood of detecting adjacent RFI-free channels to increase the signal, and therefore the thermal resolution, of the radiometer instrument. The external instrument calibration uses three targets (sky, ambient, and warm), and validation from independent stability measurements shows a mean absolute error (MAE) of 1.0 K for ambient and warm targets and 1.5 K for sky. A simple but effective RFI removal method which exploits the large number of frequency channels is also described. This method separates the desired thermal emission from RFI intrusions and was evaluated with synthetic microwave spectra generated using a Monte Carlo approach and validated with surface-based and airborne experimental measurements.

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Section: Radiometer Calibration Results and Instrument Stability Evalmentioning

confidence: 99%

Section: Calibration Measurement Procedure/post-processingmentioning

confidence: 99%

Radio-frequency interference mitigating hyperspectral L-band radiometer

Toose

Roy

Solheim³

et al. 2017

Geosci. Instrum. Method. Data Syst.

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“…Recent radio astronomy measurements at 1.4 GHz [3]- [8] have made it possible to produce maps with sufficient spatial and radiometric accuracy to be relevant for remote sensing applications [9], [10]. In this paper, a comparison is presented of background radiation predicted using the model developed by Le Vine and Abraham [9] with the measurements of several modern remote sensing radiometers.…”

Section: Introductionmentioning

confidence: 99%

Comparison of model prediction with measurements of galactic background noise at L-band

Vine

Abraham

Kerr

et al. 2005

IEEE Trans. Geosci. Remote Sensing

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Abstract-The spectral window at L-band (1.413 GHz) is important for passive remote sensing of surface parameters such as soil moisture and sea surface salinity that are needed to understand the hydrological cycle and ocean circulation. Radiation from celestial sources (mostly galactic) is strong in this window, and an accurate accounting of this background radiation is often needed for calibration. This paper presents a comparison of the background radiation predicted by a model developed from modern radio astronomy measurements with measurements made with several modern L-band remote sensing radiometers. The comparison validates the model and illustrates the magnitude of the correction necessary in remote sensing applications.Index Terms-Galactic background, microwave radiometry, remote sensing.

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“…The atmosphere is almost transparent at L-band, and the radiation contribution of the sky is minor [23]. Therefore, the contributions , , and to the received brightness temperature are not considered here.…”

Section: A Microwave Radiative Transfer Modelmentioning

confidence: 99%

L-band radiometer measurements of soil water under growing clover grass

Schwank¹,

Mätzler

Guglielmetti³

et al. 2005

IEEE Trans. Geosci. Remote Sensing

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Abstract-A field experiment with an L-band radiometer at 1.4 GHz was performed from May-July 2004 at an experimental site near Zurich, Switzerland. Before the experiment started, clover grass was seeded. Thermal infrared, in situ temperature, and time-domain reflectometer (TDR) measurements were taken simultaneously with hourly radiometer measurements. This setup allowed for investigation of the microwave optical depths and mode opacities (parallel and perpendicular to the soil surface) of the clover grass canopy. Optical depths and opacities were determined by in situ analysis and remotely sensed measurements using a nonscattering radiative transfer model. Due to the canopy structure, optical depth and opacity depend on the polarization and radiometer direction, respectively. A linear relation between vegetation water-mass equivalent and polarization-averaged optical depth was observed. Furthermore, measured and modeled radiative transfer properties of the canopy were compared. The model is based on an effective-medium approach considering the vegetation components as ellipsoidal inclusions. The effect of the canopy structure on the opacities was simulated by assuming an anisotropic orientation of the vegetation components. The observed effect of modified canopy structure due to a hail event was successfully reproduced by the model. It is demonstrated that anisotropic vegetation models should be used to represent the emission properties of vegetation. The sensitivity of radiometer measurements to soil water content was investigated in terms of the fractional contribution of radiation emitted from the soil to total radiation. The fraction of soil-emitted radiation was reduced to approximately 0.3 at the most developed vegetation state. The results presented contribute toward a better understanding of the interaction between L-band radiation and vegetation canopies. Such knowledge is important for evaluating data generated from future satellite measurements.

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Calibration error of L‐band sky‐looking ground‐based radiometers

Cited by 24 publications

References 4 publications

Radio-frequency interference mitigating hyperspectral L-band radiometer

Radio-frequency interference mitigating hyperspectral L-band radiometer

Comparison of model prediction with measurements of galactic background noise at L-band

L-band radiometer measurements of soil water under growing clover grass

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