A model-based approach to correcting spectral irradiance data using an upward-looking airborne sensor (CASI ILS)

A number of aircraft sensors have the facility to measure spectral downwelling irradiance using a sensor mounted on the roof of the aircraft, but these data are rarely used for atmospheric correction. Part of the problem is that the attitude of the airborne platform is always changing during flight, even in stable conditions, so that direct use of data from an incident light sensor (ILS) can introduce errors into atmospheric correction methods. The continual motion of the ILS is used here to advantage, as a means to fit a sky radiance distribution model developed by Brunger and Hooper (1993) to data from the Itres Instruments CASI ILS. The inclination of the ILS sensor, due to changing aircraft attitude, is considered as the slope plane in the model. The selected model coefficients correspond to parameterised atmospheric conditions and represent atmospheric transmission and the proportion of direct:diffuse flux. The method was used to correct CASI ILS data acquired over a site in southern England. Comparison with spectral irradiance measured simultaneously on the ground shows that the method reduced the variability of the ILS data and also compensated for the effect of different flight directions. The sky radiance distribution at sensor level is also calculated by the model, and shows the characteristics of the sky conditions at the time of each flight

Retrieval of at-sensor irradiance using Incident Light Sensor (ILS)

A number of aircraft sensors have the facility to measure spectral downwelling irradiance using a sensor mounted on the roof of the aircraft, but these data are rarely used for atmospheric correction. Part of the problem is that the attitude of the airborne platform is always changing during flight, even in stable conditions, so that direct use of data from an incident light sensor (ILS) can introduce errors into atmospheric correction methods. The continual motion of the ILS is used here to advantage, as a means to fit a sky radiance distribution model developed by Brunger and Hooper (1993) to data from the Itres Instruments CASI ILS. The inclination of the ILS sensor, due to changing aircraft attitude, is considered as the slope plane in the model. The selected model coefficients correspond to parameterised atmospheric conditions, i.e. clearness index and diffuse ratio. The ILS data corrected by the model are wellmatched to variations of irradiance measured at ground level during three flights. The radiance distribution at sensor level is also calculated by the model, and shows the characteristics of the sky conditions at the time of each flight

Examining the Evidence of Purchasing Power Parity by Recursive Mean Adjustment

This paper revisits the empirical evidence of purchasing power parity under the current float by the recursive mean adjustment (RMA) method (So and Shin, 1999). We first demonstrate superior finite sample performance of the RMA-based unit root test over the augmented Dickey-Fuller test via Monte Carlo experiments for 18 linear and nonlinear autoregressive data generating processes. The RMA-based unit root test rejects the null hypothesis of unit root for 16 out of 20 current float real exchange rates relative to the US dollar.We also find that the computationally simple RMA-based asymptotic confidence interval can provide useful information regarding the half-life of the real exchange rate.Recursive Mean Adjustment; Finite Sample Performance; Purchasing Power Parity; Half-Life

On the Importance of Span of the Data in Univariate Estimation of the Persistence in Real Exchange Rates

This paper revisits the empirical evidence on real exchange rates' convergence to their purchasing power parity (PPP) levels. In their recent empirical study, Murray and Papell (2002) claim that the univariate approach provides no useful information on the size of the half-lives of real exchange rate deviations from PPP. However, we obtain finite confidence intervals for the half-life for a maximum of 8 out of 16 countries by applying the nonparametric grid bootstrap technique of Hansen (1999) to over a century of real exchange rates data for 16 developed countries relative to the US dollar. Our finding sharply contrasts to that of Murray and Papell (2002) with the post Bretton Woods real exchange rates. Our finding suggests that span of the data, not the estimation methods, matters more for obtaining useful information on long-run propositions such as PPP.Median Unbiased Estimator

Official Interventions and Occasional Violations of Uncovered Interest Party in the Dollar-DM Market

This paper presents a model of exchange rate determination in which the forward premium anomaly emerges as the result of unanticipated central bank interventions in the foreign exchange market. Deviations from uncovered interest parity (UIP) therefore represent neither unexploited profit opportunities nor compensation for bearing risk. In simulations, the model generates a forward premium anomaly and matches several other notable features of US-German data. Additional empirical support is obtained from an analysis of Fed and Bundesbank interventions in the dollar--DM market where it is found that the forward premium anomaly intensifies during those times when a central bank intervenes.

A Century of Purchasing Power Parity Confirmed: The Role of Nonlinearity

Taylor (2002) claims that Purchasing Power Parity (PPP) has held over the 20th century based on strong evidence of stationarity for century-long real exchange rates for 20 countries. Lopez et al. (2005), however, found much weaker evidence of PPP with alternative lag selection methods. We reevaluate Taylor’s claim by implementing a recently developed nonlinear unit root test by Park and Shintani (2005). We find strong evidence of nonlinear mean-reversion in real exchange rates that confirms Taylor’s claim. We also find a possible misspecification problem in using the ESTAR model that may not be detected with Taylor-approximation based tests.Purchasing Power Parity; Transition Autoregressive Process; inf-t Unit Root Test

Official Interventions and Occasional Violations of Uncovered Interest Parity in the Dollar-DM Market

This paper presents a model of exchange rate determination in which the forward premium anomaly emerges as the result of unanticipated central bank interventions in the foreign exchange market. Deviations from uncovered interest parity (UIP) therefore represent neither unexploited profit opportunities nor compensation for bearing risk. In simulations, the model generates a forward premium anomaly and matches several other notable features of US-German data. Additional empirical support is obtained from an analysis of Fed and Bundesbank interventions in the dollar—DM market where it is found that the forward premium anomaly intensifies during those times when a central bank intervenesForward premium anomaly, foreign exchange intervention

Non-thermal WIMP baryogenesis

We propose a WIMP baryogensis achieved by the annihilation of non-thermally produced WIMPs from decay of heavy particles, which can result in low reheating temerature. Dark matter (DM) can be produced non-thermally during a reheating period created by the decay of long-lived heavy particle, and subsequently re-annihilate to lighter particles even after the thermal freeze-out. The re-annihilation of DM provides the observed baryon asymmetry as well as the correct relic density of DM. We investigate how wahout effects can affect the generation of the baryon asymmetry and study a model suppressing them. In this scenario, we find that DM can be heavy enough and its annihilation cross section can also be larger than that adopted in the usual thermal WIMP baryogenesis.Comment: 5 pages, 6 figure