Browsing by Subject "satelliitit"

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  • Bernhardt, P. A.; Hua, M.; Bortnik, J.; Ma, Q.; Verronen, P. T.; McCarthy, M. P.; Hampton, D. L.; Golkowski, M.; Cohen, M. B.; Richardson, D. K.; Howarth, A. D.; James, H. G.; Meredith, N. P. (Wiley Subscription Services, Inc., 2022)
    Journal of geophysical research : space physics
    Ground-based very low frequency (VLF) transmitters located around the world generate signals that leak through the bottom side of the ionosphere in the form of whistler mode waves. Wave and particle measurements on satellites have observed that these man-made VLF waves can be strong enough to scatter trapped energetic electrons into low pitch angle orbits, causing loss by absorption in the lower atmosphere. This precipitation loss process is greatly enhanced by intentional amplification of the whistler waves using a newly discovered process called rocket exhaust driven amplification (REDA). Satellite measurements of REDA have shown between 30 and 50 dB intensification of VLF waves in space using a 60 s burn of the 150 g/s thruster on the Cygnus satellite that services the International Space Station. This controlled amplification process is adequate to deplete the energetic particle population on the affected field lines in a few minutes rather than the multi-day period it would take naturally. Numerical simulations of the pitch angle diffusion for radiation belt particles use the UCLA quasi-linear Fokker Planck model to assess the impact of REDA on radiation belt remediation of newly injected energetic electrons. The simulated precipitation fluxes of energetic electrons are applied to models of D-region electron density and bremsstrahlung X-rays for predictions of the modified environment that can be observed with satellite and ground-based sensors.
  • Lindfors, Anders; Riihelä, Aku; Aarva, Antti; Latikka, Jenni; Kotro, Janne (Ilmatieteen laitos, 2014)
    Raportteja - Rapporter - Reports ; 2014:5
  • Vihervaara, Petteri; Kullberg, Peter; Hurskainen, Pekka (2019)
    Futura 3/2019
    Our planet is undergoing massive global change. We are increasingly aware of the biodiversity crisis, which raises concerns about the future of nature and humankind. Targets and goals set at several multilateral environmental agreements to stop the crisis have been agreed upon, but their effective follow-up and implementation require relevant and timely biodiversity data. For this purpose, a set of policy-relevant Essential Biodiversity Variables (EBVs), describing the biological state and capturing the major dimensions of biodiversity change, have been proposed. Generating EBVs requires integration of in situ and Earth observation data. The former is collected in the field by experts, citizens, or automatic sensor networks, assisted by new technologies such as eDNA and machine learning, while the latter is measured from space or air, enabled by analysis-ready multi-sensor data and cloud computing services. As a case example for better biodiversity monitoring, the Finnish Ecosystem Observatory (FEO) is proposed. FEO will combine and standardize environmental information from different data sources, making the data, metadata and models openly available and easily accessible to users and policy makers.
  • Manninen, Terhikki; Jääskeläinen, Emmihenna; Siljamo, Niilo; Riihelä, Aku; Karlsson, Karl-Göran (Copernicus Publications, 2022)
    Atmospheric measurement techniques
    This paper describes a new method for cloudcorrecting observations of black-sky surface albedo derived using the Advanced Very High Resolution Radiometer (AVHRR). Cloud cover constitutes a major challenge for surface albedo estimation using AVHRR data for all possible conditions of cloud fraction and cloud type with any land cover type and solar zenith angle. This study shows how the new cloud probability (CP) data to be provided as part of edition A3 of the CLARA (CM SAF cLoud, Albedo and surface Radiation dataset from AVHRR data) record from the Satellite Application Facility on Climate Monitoring (CM SAF) project of EUMETSAT can be used instead of traditional binary cloud masking to derive cloud-free monthly mean surface albedo estimates. Cloudy broadband albedo distributions were simulated first for theoretical cloud distributions and then using global cloud probability (CP) data for 1 month. A weighted mean approach based on the CP values was shown to produce very-high-accuracy black-sky surface albedo estimates for simulated data. The 90 % quantile for the error was 1.1 % (in absolute albedo percentage) and that for the relative error was 2.2 %. AVHRR-based and in situ albedo distributions were in line with each other and the monthly mean values were also consistent. Comparison with binary cloud masking indicated that the developed method improves cloud contamination removal.
  • Pitkänen, Timo P.; Sirro, Laura; Häme, Lauri; Häme, Tuomas; Törmä, Markus; Kangas, Annika (ScienceDirect, 2020)
    International Journal of Applied Earth Observation and Geoinformation 86 (2020)
    The majority of the boreal forests in Finland are regularly thinned or clear-cut, and these actions are regulated by the Forest Act. To generate a near-real time tool for monitoring management actions, an automatic change detection modelling chain was developed using Sentinel-2 satellite images. In this paper, we focus mainly on the error evaluation of this automatized workflow to understand and mitigate incorrect change detections. Validation material related to clear-cut, thinned and unchanged areas was collected by visual evaluation of VHR images, which provided a feasible and relatively accurate way of evaluating forest characteristics without a need for prohibitively expensive fieldwork. This validation data was then compared to model predictions classified in similar change categories. The results indicate that clear-cuts can be distinguished very reliably, but thinned stands exhibit more variation. For thinned stands, coverage of broadleaved trees and detections from certain single dates were found to correlate with the success of the modelling results. In our understanding, this relates mainly to image quality regarding haziness and translucent clouds. However, if the growing season is short and cloudiness frequent, there is a clear trade-off between the availability of good-quality images and their preferred annual span. Gaining optimal results therefore depends both on the targeted change types, and the requirements of the mapping frequency.
  • Oja, Heikki; Westman, Juhani (Gummerus, 1975)
  • Sundström, Anu-Maija; Virta, Henrik; Ialongo, Iolanda; Tamminen, Johanna (2020)
    Raportteja - Rapporter - Reports ; 2020:1
    Tässä selvityksessä kartoitetaan ensimmäistä kertaa satelliittimittausten hyödyntämistä ilmanlaadun seurannassa Suomessa. Satelliittien ehdottomana vahvuutena on ilmanlaatumuuttujien alueellisen jakauman kuvaaminen sekä ilmansaasteiden kulkeutumisen seuranta, joita tässä työssä on demonstroitu käyttämällä alailmakehän typpidioksidi (NO2}-havaintoja TROPOspheric Monitoring Instrument (TROPOMI) ja Ozone Monitoring Instrument (OMI) satelliitti-instrumenteista. TROPOMI laukaistiin EU:n Copernicus-ohjelman rahoittamassa Sentinel-5P satelliitissa vuonna 2017, ja se on tällä hetkellä paikalliselta erotuskyvyltään tarkin ilmanlaadun kannalta oleellisia kaasuja havainnoiva satelliittimittalaite. Suomalais-hollantilainen OMI-instrumentti NASAn Aura-satelliitissa on puolestaan tuottanut maailmanlaajuisia havaintoja jo lähes 15 vuoden ajan. Tämän työn tulokset näyttävät, että satelliittien avulla voidaan tarkastella typpidioksidin alueellista jakaumaa Suomessa sekä lähialueilla aina kaupunkitasolle asti. Esimerkiksi pääkaupunkiseudun keskimääräisissä pitoisuuksissa voidaan erottaa alueellisia vaihteluita ja nähdä selvä ero viikonpäivien ja viikonloppujen välillä. OMI-instrumentin havainnoista puolestaan nähdään, että alailmakehän NO2-pitoisuudet ovat keskimäärin laskeneet koko maassa vuodesta 2005 vuoteen 2018. Keskeisimpiä kysymyksiä satelliittidatan hyödyntämisessä ilmanlaadun seurannassa on se, kuinka hyvin satelliittihavainnot vastaavat in situ -mittauksista nähtyjä vaihteluita. Vertailu TROPOMI-havaintojen ja pintamittausten välillä näyttää, että vaikka kaupungin sisällä yksittäisten asemien kohdalla yhteensopivuus voi vaihdella asemittain, korrelaatio on hyvä kun vastaavuutta tarkastellaan yhdistämällä kunkin kaupungin keskustan pintahavainnot. Tulos on samansuuntainen sekä Suomessa että myös muualla Euroopassa.