SMEX04/NAME Soil Moisture Remote Sensing Field Experiment Status Report 11/6/03

Rationale One of the main objectives of NAME is to improve prediction of warm season precipitation. Warm season precipitation is highly dependent on convection which, in turn, is controlled, at least in part, by soil moisture and surface temperature. Therefore, an accurate characterization of spatial and temporal variability of soil moisture is critical to NAME. Given the spatial scales involved, remote sensing is the only realistic strategy to provide soil moisture maps based on observations.

1.The spatial and temporal patterns of soil moisture estimated from remote sensing (by aircraft so as to provide high spatial resolutions) can be used for initialization and/or updating of the boundary conditions for the land surface component of land-atmosphere models. 2.The spatial and temporal patterns of soil moisture can be used for validation of land surface model outputs, and to discern the relationship between soil moisture and warm season precipitation and associated feedback mechanisms. 3.Aircraft-based soil moisture mapping can provide a basis for model-based extrapolation over Tier 1, using methods developed under LDAS. For the larger Tier 2 and 3 regions, satellite retrievals (AMSR), tested using aircraft data, will be appropriate and span several AMSR grid cells.

Strategy Aircraft remote sensing (C- and L-band passive microwave) transects over well instrumented surface sites (including continuous soil moisture sensing at points, and many additional gravimetric samples) for two target areas of very roughly 10 4 km 2 each, one north (Walnut Gulch) and one south (Sonora area) of the U.S.-Mexico border Use the in situ observations to verify the aircraft estimates over the target areas, and the mapped aircraft estimates in turn to “train” algorithms to produce maps of soil moisture over (at least) NAME Tier 1 from satellite products (specifically AMSR flying on board Aqua) This approach has previously been used in a series of SGP and SMEX field campaigns. A significant difference of the NAME target areas is complex topography Funding for the soil moisture field campaign has been provided by NASA Terrestrial Hydrology Program

Soil Moisture Experiments (SMEX) Science – Water Cycle – Algorithms – Validation – Technology Aircraft Instruments – PSR – ESTAR/2DSTAR – GPS Satellite Instruments – AMSR-E – – SSM/I – TMI – Envisat, ERS-2, Quikscat – Coriolis – MODIS, ASTER – TM – GOES, AVHRR Sites (June-July) – Oklahoma – Georgia – Alabama – Brazil Ground Investigations – Soil moisture – Soil temperature – Surface flux – Vegetation – Surface roughness – Ground based radiometry – Insitu calibration – Insitu scaling AIRSAR – Iowa Arizona Mexico – – – Sites (How we put our experiments together)

In much of the interior of the North American continent, summer precipitation is a dominant feature of the annual cycle. Surface boundary conditions play an important role in initiation and maintenance of the North American Monsoon System (NAMS), which controls summer precipitation over much of this region. Understanding these processes is a focus for the North American Monsoon Experiment (NAME) A working hypothesis of NAME is that among the land surface antecedent boundary conditions that control the onset and intensity of the NAMS is soil moisture. The influence of the land surface is relayed through surface evaporation and associated surface cooling (dependent on soil moisture), terrain, and vegetation cover. Soil moisture and, in particular, surface wetness, can change dramatically after heavy rain events. Increased soil moisture after precipitation promotes evapotranspiration between storm events. This may contribute to enhanced convection and further precipitation. As part of NAME there will be an intensive observing period in the summer of 2004 over the Tier I domain. The intention of SMEX04-NAME is to enhance the terrestrial hydrology component of NAME by facilitating development of soil moisture. Specific activities include the provision of soil moisture products from the existing insitu network in Arizona and the development of an equivalent network within a study region in Mexico, and soil moisture products derived from existing satellite sensors on Aqua and TRMM. An intensive ground and aircraft field campaign will take place between mid July and mid August 2004 that will provide validation of the insitu and satellite products. SMEX04-NAME will also address important algorithm and validation issues for existing satellite based soil moisture products from the Advanced Microwave Scanning Radiometer and

Soil Moisture Observations and Products for NAME Over much of the NAME region soil moisture observations are sparse. Remote sensing provides an alternative means of observing spatial and temporal variations in surface wetness over the region. Frequent derived estimates of soil moisture over much of the NAME region should be made possible through recently launched satellite microwave sensors, including the Advanced Microwave Scanning Radiometer (AMSR) both on Aqua (NASA) and ADEOS-II (NASDA) as well as the TRMM Microwave Imager

Examples of Aircraft and Satellite Soil Moisture Products Aircraft based Polarimetric Scanning Radiometer (PSR) from SMEX02 (Iowa). Uses the same C band channel as AMSR. Spatial resolution of 2 km. Satellite based TRMM Microwave Imager brightness temperature images for a sequence of days over the Tier 1 region.

SMEX02 (Iowa) Soil moisture Products from the Aircraft Based PSR Easting (m) Northing (m) Soil moisture (%)

Regional study areas 50 by 75 km linked to Ease-grid 25 km cells SMEXS04/NAME soil moisture experiment target areas

Walnut Gulch Regional Study Area (WG) Red markers are the corners of the 25 km Ease Grid cells

Mexico Regional Study Area (MX) Red markers are the corners of the 25 km Ease Grid cells

SMEX04 Elements In-situ soil moisture networks, precipitation, and micromet measurements (north and south sites) Aircraft mapping Intensive sampling concurrent with aircraft mission Satellite products

SMEX04 Elements: In-situ soil moisture networks Modeled after current AMSR Cal/Val project 12 or more long term in-situ sites All sites have 5 cm soil moisture and temperature (Vitel Hydraprobe) and precipitation Walnut Gulch is already instrumented A region in Mexico is being instrumented (Chris Watts)

Walnut Gulch Soil Moisture Sites

SMEX04 Elements: Aircraft Overview NASA JSC WB-57 July 15 – August 15, 2004 Aircraft sensors –PSR and an L band Mission –15 flight dates, 5 hours per day –Walnut Gulch and Mexico sites (50 by 100 km) –4 flightlines per site Aircraft to be based in Tucson Discussions underway (via NASA) for flight clearances (and some issues related to border radars)

NASA JSC WB57 Aircraft

SMEX04 Elements: Intensive Sampling Concurrent with Aircraft Mission Calibration of network Fills in the spatial domain Two teams (Walnut Gulch and Mexico) Mexico partnership with local institutions Soil moisture retrieval algorithms will be variation of the one developed for SMEX02 and SMEX03

SMEX04 Available Satellite Products Satellite sensors: AMSR (Aqua) Coriolis TMI SSM/I

Status Core team formed: HRSL, JPL, ARS Tucson, IMADES (Mexico), Univ. Arizona Aircraft identified: WB57 PSR being adapted L band TBD Team Workshop (onsite and telecon) For details: hydrolab.arsusda.gov/smex04/

Outstanding issues Adaptation of L-band instrument (probably ESTAR or 2D-STAR) to fly on WB57 (cost and timing) Ancillary measurements (e.g. latent and sensible heat flux) in south would be highly desirable, requires aircraft team and/or flux tower. Could this be coordinated with Douglas-Watts activities further south? Coordination of rain gauge and other in situ data collection with activities elsewhere in Tier 1 (e.g. common archiving of precipitation data?) Coordination of aircraft clearances with NOAA aircraft being flown elsewhere Identification of ground teams Planned workshop (Tucson Feb 2004) will address many of these issues For details: hydrolab.arsusda.gov/smex04/