Skylab L-band microwave radiometer observations of soil moisture revisited.

In preparing for future L-band passive microwave soil moisture satellite missions, investigators have employed ground, aircraft and satellite sensors. Of the satellite sensors, there has been only one instrument that provides any heritage at L-band: the Skylab S-194 instrument that operated in the 1970s. Here a dataset from the S-194 was located and recovered. Data from these Skylab missions have been analysed and reported in a few applications, however, these studies utilized limited validation and exploited only a portion of the data collected. In this investigation we explored the use of products from climate model reanalysis projects as ancillary or alternative validation data. Analyses showed that the reanalysis outputs were not accurate and would be of limited value. Tests using a radiative transfer based soil moisture retrieval algorithm matched the observations available for validation. These results support the use of this approach as a tool in understanding a wider range of vegetation condition effects on soil moisture retrieval. © 2004 Taylor and Francis Ltd

Evaluation of soil moisture from satellite observations over South America

A study was performed to evaluate the surface soil moisture derived from Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) sensor observations over South America. Other soil moisture and rainfall datasets were also used for the analysis. The information for the soil data came from the Eta regional climate model, and for the rainfall data from the Tropical Rainfall Microwave Mission (TRMM) satellite. Statistical analysis was used to evaluate the quality of the soil moisture and rainfall products, with estimates of the correlation coefficient (R),

Variação do regime de umidade do solo durante o ciclo fenológico de plantas de batata

Neste trabalho foram analisadas as relações entre a produção, o desenvolvimento vegetativo e a evapotranspiração de uma cultura de batata (Solanum tuberosum L.) submetida à três regimes de umidade, definidos pelos valores assumidos pelo potencial matricial da água do solo antes de se proceder as irrigações (-0,5; -1,0 e -5,0 bares) em três estádios de desenvolvimento das plantas. Com respeito à produção de tubérculos, ficou evidenciado que por ocasião da tuberização e desenvolvimento de um grande número de tubérculos, as plantas revelaram uma maior sensibilidade à redução da umidade do solo. Assim, ocorrendo deficits moderados (-1,0 bar) no período inicial de desenvolvimento, a produção não foi significativamente afetada. Isto foi atribuído, em parte, à recuperação parcial do crescimento vegetativo no estádio subseqüente, quando foram restabelecidas condições mais adequadas de umidade no solo. O mesmo não se verificou no tratamento submetido a deficits mais severos (-5,0 bares) no estádio inicial. Neste caso, o crescimento foi quase irreversivelmente reduzido, contribuindo para diminuir a produção e a eficiência de utilização de água pelas plantas. A redução da umidade do solo, a partir dos 60 dias após a emergência das plantas, não afetou a produção de tubérculos. Este procedimento concorreu para aumentar significativamente a eficiência de utilização de água. Além disso, havendo suspensão total da irrigação neste período, a senescência foi antecipada em 16 dias, em relação aos tratamentos submetidos a níveis de umidade mais elevados. O desenvolvimento vegetativo e a produção não foram igualmente afetados pela redução da umidade do solo. Conseqüentemente, o crescimento das plantas não parece se constituir em um índice absoluto da produção de tubérculos de batata.Changes in soil water regime during vegetative growth and yield production of potato crop was not equally affected by soil water depletion. Concerning to yield production the results show that the soil water depletion effect are closely related to intensity and duration of water deficits and stage of plant growth in which they occurs. So, it was stablished that during the stage of tuberization and tuber development, the plant exhibited higher sensibility to water deficiency than in the initial or final stage of plant growth. On the other hand, moderate deficits (-1.0 bar of soil water matric potential) occurring in the initial stage of plant growth did not have any effect in tuber yield. This was attributed to the resumption of growth in the following stage. However, when a more severe water deficiency occurred (-5.0 bars of soil water matric potential), it was not observed the resumption phenomenon. In this case, an irreversible decrease in growth had the effect of decreasing yield. Soil moisture depletion in the final growth stage, about 60 days after plant emergence, did not decrease tuber yield, which increased plant water efficiency. When water supply was suppressed in this stage, the senescence was hastened in 16 days when compared to the other treatments with higher levels of soil moisture. As was evidenced, the vegetative growth is not an absolute index of the potato yield production